Full opinion text
RALPH B. GUY, Jr., Circuit Judge, on rehearing. A number of persons, including these plaintiffs, who either lived or owned property near defendant’s landfill, brought a class action for personal injuries and property damage resulting from hazardous chemicals leaking from the landfill and contaminating the local water supply. The district court held the corporation liable upon legal theories of strict liability, common law negligence, trespass, and nuisance. The court awarded five representative members of the class compensatory damages for their personal injuries, as well as property damages, plus prejudgment interest on the entire award. The district court further held the corporation liable to the class as a whole for punitive damages. Upon a review of the lengthy record in this difficult case, we find that the district court properly held Velsicol liable to the five representative plaintiffs but erred in the nature and amount of the damage awards. Accordingly, we affirm in part, reverse in part, and remand with directions for recalculation of some of the damages. I. FACTS In August, 1964, the defendant, Velsicol Chemical Corporation (Velsicol), acquired 242 acres of rural land in Hardeman County, Tennessee. The defendant used the site as a landfill for by-products from the production of chlorinated hydrocarbon pesticides at its Memphis, Tennessee, chemical manufacturing facility. Before Velsicol purchased the landfill site and commenced depositing any chemicals into the ground, it neither conducted hydrogeological studies to assess the soil composition underneath the site, the water flow direction, and the location of the local water aquifier, nor drilled a monitoring well to detect and record any ongoing contamination. From October, 1964, to June, 1973, the defendant deposited a total of 300,000 55-gallon steel drums containing ultrahazardous liquid chemical waste and hundreds of fiber board cartons containing ultrahazardous dry chemical waste in the landfill. Shortly after Velsicol began its disposal operations at the landfill site, local residents and county, state, and federal authorities became concerned about the environmental impact of the defendant’s activities. As a result of this concern, the United States Geological Survey (USGS), in 1967, prepared the first of several reports on the potential contamination effects of the chemicals deposited into the landfill up to that time. The 1967 report indicated that chlorinated hydrocarbons had migrated down into the subsoil and had contaminated portions of the surface and subsurface environment adjacent to the disposal site. While the chemicals had not reached the local water aquifer, the USGS concluded that both the local and contiguous ground water were in danger of contamination. Subsequent to publication of the 1967 USGS report, Velsicol expanded the size of the landfill disposal site from twenty to forty acres. State authorities increasingly became concerned about the defendant’s disposal of ultrahazardous chemicals at the site. In 1972, the state filed an administrative action to close the landfill because the chlorinated hydrocarbons buried at the site allegedly were contaminating irreparably the subsurface waters. The state ordered Vel-sicol to cease disposal of all toxic chemicals by August 21,1972, and all other chemicals by June 1, 1973. In 1976, three years after the state permanently closed the landfill disposal site, the USGS, in conjunction with state authorities, commenced updating the 1967 USGS report. One major concern, which gave rise to the new USGS study, was the possibility of the chemicals migrating toward wells utilized by local residents. In 1978, the USGS issued a written report detailing the 1976 update of the 1967 report. The 1978 report found that the water table of the local aquifer was highly contaminated. The 1978 USGS report also indicated that the local aquifer moved toward the northwest, north, and northeast, rather than just toward the east as earlier indicated in the 1967 USGS report. Consequently, residents’ wells, which were previously presumed safe from contamination, were now potentially polluted. In view of the continued complaints by numerous local residents, the Department of Health conducted further well water sampling tests in 1978. These tests revealed the presence of certain chlorinated hydrocarbons in numerous wells. Additionally, in 1978, the state, the USGS, the EPA, and Velsicol all commenced numerous extensive ground water surveys of the site and surrounding area. The surveys collectively identified twelve to fifteen drinking water wells, which were adjacent to the site, as contaminated with high levels of chlorinated hydrocarbons. Specifically, the surveys established that six of these wells were contaminated by carbon tetrachloride in excess of 100 parts per billion and high amounts of chloroform. The users of these wells, and all wells within 1,000 acres around the landfill site, were advised to stop using them for any purpose. In 1978, forty-two plaintiffs sued Velsicol in the Circuit Court of Hardeman County, Tennessee, on behalf of themselves and all others similarly situated for damages and injunctive relief. The complaint sought $1.5 billion in compensatory damages and $1 billion in punitive damages. The defendant removed the action to the United States District Court for the Western District of Tennessee, alleging diversity of citizenship and the requisite amount in controversy. Shortly after removal, all but fifteen of the original forty-two plaintiffs settled their claims. Plaintiffs’ counsel filed an amended complaint for damages and injunctive relief and added forty-seven new plaintiffs to the original lawsuit pursuant to Fed.R. Civ.P. 20(a). The complaint sought relief for involuntary exposure to certain chemical substances known to cause cancer, affect the central nervous system and permanently damage other organs of the human body, and for loss of value to their real property in the region affected by the chemicals. Additionally, seven individual civil actions involving fourteen plaintiffs were instituted against Velsicol alleging that the defendant negligently disposed of toxic chemical wastes. The district court, on its own motion and over the defendant’s objection, certified a Fed.R.Civ.P. 23(b)(3) class action thereby consolidating the separate lawsuits. Thereafter, the plaintiffs’ counsel filed a list of class action participants. At this time, the district court directed the plaintiffs’ counsel to designate five representative plaintiffs whose claims were to be tried in the first instance to establish liability and damages on their individual claims, liability to the entire class, and punitive damages, if any. The class action proceeded to trial with the five representative plaintiffs proposed by the plaintiffs’ counsel (Steven Sterling, Daniel Johnson, Curry Ivy, James Wilbanks, and James Maness, Jr.). After a bench trial of the five claims, the district court found Velsicol liable to the plaintiffs on legal theories of strict liability, common law negligence, trespass, and nuisance. The court concluded that the defendant’s hazardous chemicals, which escaped from its landfill and contaminated plaintiffs’ well water, were the proximate cause of the representative plaintiffs’ injuries. The district court awarded the five individuals compensatory damages total-ling $5,273,492.50 for their respective injuries, plus prejudgment interest dating back to July, 1965, of $8,964,973.25. All damages, except for $48,492.50 to one plaintiff for property damage claims, were awarded for personal injuries. The district court also awarded $7,500,000 in punitive damages to the class as a whole. The court deferred to individual hearings, to be held after trial, the issues of causation and injury of any other persons purporting to be members of the class entitled to share in this award. On appeal, the defendant argues that the district court lacked subject matter jurisdiction over the class members and impermis-sibly certified the case as a class action. The defendant further argues the district court erred in finding that the plaintiffs were exposed to its chemicals and that there was a causal connection between their exposure, if any, and their resultant injuries. Accordingly, the defendant asserts the district court improperly awarded compensatory damages to the plaintiffs for their alleged injuries. Defendant also asserts that prejudgment interest on the compensatory award and punitive damages should not have been awarded. We address the defendant’s arguments seriatim. II. SUBJECT MATTER JURISDICTION The defendant argues that the district court lacked subject matter jurisdiction over all but two of the representative class plaintiffs. Velsicol states the remaining three representative plaintiffs, and all other putative class members, never formally filed any pleadings specifically alleging and justifying that the amount of controversy between each of them and the defendant exceeded $10,000. Velsicol further asserts that, once it challenged the district court’s jurisdiction over these plaintiffs, the court was obligated to consider immediately the sufficiency of each plaintiff’s claim and dismiss all of those plaintiffs unable to demonstrate a valid claim at that time. In the instant case, Velsicol filed two separate Fed.R.Civ.P. 12(b)(1) dismissal motions prior to trial. Defendant moved to dismiss all absent plaintiffs who, though they received class action notification, failed to comply with the class certification order and allege claims in excess of the requisite jurisdictional amount. The defendant also moved to dismiss those plaintiffs who subsequently joined in the class action pursuant to Fed.R.Civ.P. 20(a) but failed to assert claims in excess of $10,000 each. The plaintiffs’ counsel responded that all of the representative class plaintiffs and designated class members each asserted a claim in excess of the requisite amount. Counsel reasoned that each of the original plaintiffs claimed an amount far in excess of $10,000 in the ad damnum clause of their amended complaint. Therefore, each of the remaining plaintiffs, who became part of the class action by not opting out, adopted the ad damnum provision. At a pretrial hearing, the district court decided that the defendant’s motion as to the representative class members would be determined at trial and deferred the decision as to all other class members until a later date. The trial commenced on June 21, 1982. In a September 16, 1985 consent order, which recertified the class and identified 128 individuals including the five representative plaintiffs as members of the class, the court stated that: recertification and reduction of the number in a class merely constitutes a prima facie finding by this Court that those persons named ... can in good faith state a claim in excess of $10,000. Subsequently, the court held in its August 1, 1986 opinion that the proper pleadings, jurisdictional amount, and notice requirements of the representative class members had been properly complied with in all respects and were indicative of the remaining party plaintiffs’ claims. Each of the representative plaintiffs were awarded compensatory damages far in excess of $10,000. Defendant properly argues that, in accordance with Zahn v. International Paper Co., 414 U.S. 291, 94 S.Ct. 505, 38 L.Ed.2d 511 (1973), and Amen v. City of Dearborn, 532 F.2d 554 (6th Cir.1976), appealed on other grounds, 718 F.2d 789 (6th Cir.1983), cert. denied, 465 U.S. 1101, 104 S.Ct. 1596, 80 L.Ed.2d 127 (1984), each plaintiff in a class action individually must allege a claim in excess of $10,000. Likewise, a judgment may be vacated at any time, even on appeal, for lack of subject matter jurisdiction. See Persinger v. Islamic Republic of Iran, 729 F.2d 835 (D.C.Cir.), cert. denied, 469 U.S. 881, 105 S.Ct. 247, 83 L.Ed.2d 185 (1984); Basso v. Utah Power & Light Co., 495 F.2d 906 (10th Cir.1974); Canadian Indemnity Co. v. Republic Indemnity Co., 222 F.2d 601 (9th Cir.1955). However, defendant erroneously asserts that once it challenges the district court’s jurisdiction with respect to the amount in controversy for each class member, the court must make an immediate determination of the sufficiency of each claim. Fed.R.Civ.P. 12(d) provides that: The defenses specifically enumerated (1)-(7) in subdivision (b) of this rule, whether made in a pleading or by motions ... shall be heard and determined before trial on application of any party unless the court orders that the hearing and determination thereof be deferred until the trial. (Emphasis added). The method and timetable for deciding a Rule 12(b) motion under Rule 12(d) is left to the sole discretion of the trial judge who may defer that determination until trial. In response to defendant’s Rule 12(b) motions, the plaintiffs’ counsel repeatedly asserted that each class member alleged a claim in excess of the requisite jurisdictional amount. In determining whether a dismissal is justified for lack of the jurisdictional amounts, the sums posited by the plaintiffs, provided they are made in good faith, control unless it appears to a legal certainty that their claims are, in actuality, for less. St. Paul Mercury Indemnity Co. v. Red Cab Co., 303 U.S. 283, 58 S.Ct. 586, 82 L.Ed. 845 (1938). Vel-sicol failed either to assert that the plaintiffs proffered bad faith damage claims or to set forth any basis for justifying its allegation that the plaintiffs’ claims were for less than the jurisdictional amount. Rather, Velsicol charges the district court with “policing” the sufficiency of each plaintiffs claim. Absent some apparent reason for delving into the substance of the plaintiffs’ posited claims, the district court is not saddled with such an affirmative obligation. The district court stated, in both its consent order and subsequent opinion, that each of the representative and remaining putative class members posited good faith claims in excess of $10,000. Consequently, while it might have been preferable to have addressed the defendant’s dismissal motions far earlier in the course of the proceeding, we cannot say that the district court improperly exercised its jurisdiction over the representative and remaining class members. III. CLASS ACTION CERTIFICATION Velsicol argues that the district court improperly certified this case as a Fed.R. Civ.P. 23(b)(3) class action because common questions of law or fact did not predominate over individual questions. As to the requirements necessary for certification of a Rule 23(b)(3) class action, the district court held in its February 12, 1981 certification order that (1) the class was so large that joinder of all members was impractical (Rule 23(a)(1)), (2) there were questions of law or fact common to the class (Rule 23(a)(2)), (3) representative claims were typical of the claims of the class (Rule 23(a)(3)), and (4) the representative parties would fairly and adequately protect the interests of the class (Rule 23(a)(4)). The court further found that questions of law or fact common to the members of the class predominated over any questions affecting only individual members and that a class action would be superior to other available methods for the fair and efficient adjudication of the controversy (Rule 23(b)(3)). The procedural device of a Rule 23(b)(3) class action was designed not solely as a means for assuring legal assistance in the vindication of small claims but, rather, to achieve the economies of time, effort, and expense. See, e.g., Hernandez v. Motor Vessel Skyward, 61 F.R.D. 558 (S.D.Fla.1973), aff'd without opinion, 507 F.2d 1278 (5th Cir.1975); Buford v. American Finance Co., 333 F.Supp. 1243 (N.D.Ga.1971). See also Fed.R.Civ.P. 1. However, the problem of individualization of issues often is cited as a justification for denying class action treatment in mass tort accidents. While some courts have adopted this justification in refusing to certify such accidents as class actions, numerous other courts have recognized the increasingly insistent need for a more efficient method of disposing of a large number of lawsuits arising out of a single disaster or a single course of conduct. In mass tort accidents, the factual and legal issues of a defendant’s liability do not differ dramatically from one plaintiff to the next. No matter how individualized the issue of damages may be, these issues may be reserved for individual treatment with the question of liability tried as a class action. Consequently, the mere fact that questions peculiar to each individual member of the class remain after the common questions of the defendant’s liability have been resolved does not dictate the conclusion that a class action is impermissible. The district court retains broad discretion in determining whether an action should be certified as a class action, and its decision, based upon the particular facts of the case, should not be overturned absent a showing of abuse of discretion. See Hopper v. Schweiker, 596 F.Supp. 689 (M.D.Tenn.1984), aff'd, 780 F.2d 1021 (6th Cir.1985), cert. denied, 475 U.S. 1111, 106 S.Ct. 1522, 89 L.Ed.2d 920 (1986); Kentucky Educators Public Affairs Council v. Kentucky Registry of Election Finance, 611 F.2d 1125 (6th Cir.1982); Cross v. National Trust Life Insurance Co., 553 F.2d 1026 (6th Cir.1977). In complex, mass, toxic tort accidents, where no one set of operative facts establishes liability, no single proximate cause equally applies to each potential class member and each defendant, and individual issues outnumber common issues, the district court should properly question the appropriateness of a class action for resolving the controversy. However, where the defendant’s liability can be determined on a class-wide basis because the cause of the disaster is a single course of conduct which is identical for each of the plaintiffs, a class action may be the best suited vehicle to resolve such a controversy- In the instant case, each class member lived in the vicinity of the landfill and allegedly suffered damages as a result of ingesting or otherwise using the contaminated water. Almost identical evidence would be required to establish the level and duration of chemical contamination, the causal connection, if any, between the plaintiffs’ consumption of the contaminated water and the type of injuries allegedly suffered, and the defendant’s liability. The single major issue distinguishing the class members is the nature and amount of damages, if any, that each sustained. To this extent, a class action in the instant case avoided duplication of judicial effort and prevented separate actions from reaching inconsistent results. with similar, if not identical, facts. The district court clearly did not abuse its discretion in certifying this action as a Rule 23(b)(3) class action. However, individual members of the class still will be required to submit evidence concerning their particularized damage claims in subsequent proceedings. IV. PROXIMATE CAUSATION The main thrust of Velsieol’s argument on appeal is that there was insufficient evidence to support a finding of causation between its disposal of toxic chemicals and plaintiffs’ injuries. Velsicol further argues that the various types of injuries identified by the district court were based upon im-permissibly speculative and conjectural evidence. In accordance with Fed.R.Civ.P. 52(a), a finding is clearly erroneous when “although there is evidence to support it, the reviewing court on the entire evidence is left with the definite and firm conviction that a mistake has been committed.” United States v. Oregon State Medical Society, 343 U.S. 326, 339, 72 S.Ct. 690, 698, 96 L.Ed. 978 (1952); United States v. United States Gypsum Co., 333 U.S. 364, 395, 68 S.Ct. 525, 541, 92 L.Ed. 746 (1948). However, if the district court’s account of the evidence is plausible in light of the record viewed in its entirety, we may not reverse it even though convinced that had we been sitting as the trier of fact, we would have weighed the evidence differently. United States v. Yellow Cab Co., 338 U.S. 338, 342, 70 S.Ct. 177, 179, 94 L.Ed. 150 (1949). Indeed, the reviewing court oversteps the bounds of its duty under Fed.R.Civ.P. 52(a) if it undertakes to duplicate the role of the lower court. Anderson v. City of Bessemer, 470 U.S. 564, 105 S.Ct. 1504, 84 L.Ed.2d 518 (1985). A district court’s ultimate and subsidiary findings concerning causation, negligence, nuisance, trespass, actual damages, and punitive damages, are all factual determinations included within the scope of Rule 52(a). This is even clearer when the trial involves technical or scientific issues. Velsicol argues that proof of the plaintiffs’ exposure to its chemicals and the causal connection between that exposure, if any, and their subsequent injuries imper-missibly was based upon insufficient evidence. Specifically, the defendant asserts that there was no evidence that two known carcinogens (carbon tetrachloride and chloroform) were in the plaintiffs’ wells in the late 1960’s and early 1970’s when they allegedly were consuming the contaminated water. To overcome this lack of evidence, Velsicol contends that the plaintiffs introduced into evidence an invalid water computing model that erroneously concluded that the plaintiffs were exposed to significant levels of contaminants as early as 1970. By extrapolation, the plaintiffs’ model purported to show that dramatically high concentrations of carbon tetrachloride and chloroform were in the plaintiffs’ wells as early as 1970 and, therefore, that the plaintiffs had been exposed to the chemical contaminants in sufficiently high dosages for a prolonged period of time sufficient to cause their resultant injuries. On appeal, the defendant not only questions the validity of ground water modeling techniques in general, but also argues that plaintiffs’ particular model fatally failed to utilize all of the relevant data. We reject both of Velsicol’s arguments. Numerous courts have validated water modeling techniques to predict past levels of contamination in drinking water where the model was both properly conceived and constructed. See e.g., Anderson v. W.R. Grace & Co., 628 F.Supp. 1219 (D.Mass.1986). The plaintiffs carefully devised, calibrated, and tested their model, based upon physical data generated by Velsicol’s own consultants, to determine the physical and chemical characteristics beneath the landfill. They properly formulated the various components of the model (the determination of transmissivity, the infiltration rate, the water table configuration, the porosity, the dispersion coefficient, and the ground water velocity) and utilized all relevant data. The plaintiffs’ failure to incorporate selected well samplings conducted after 1978 necessarily does not invalidate their model and the conclusions to be drawn therefrom. In 1978, the EPA tested nineteen of twenty-two domestic wells (not including four USGS wells) for chemical contamination. After 1978, only one of the five wells from which the representative plaintiffs drank or otherwise used water and seven of the nineteen remaining wells were ever again tested. Data showing the level of chemical contamination of these remaining wells was available only upon a limited and sporadic basis. While the plaintiffs did not incorporate these post-1978 well samplings into their model, they thoroughly reviewed and utilized the data to confirm the water table contour component of their model. Plaintiffs also did not utilize soil column studies, such studies having been abandoned by Velsicol itself and found non-credible by the district court. However, the plaintiffs utilized all other relevant data including, but not limited to, the 1964 Rima Study, the 1978 Sprinkle Study, the data generated by the State of Tennessee in 1970, all the information generated by AWARE, and all of the monitoring information by Velsicol, the State of Tennessee, and the EPA. Because the district court carefully considered the plaintiffs’ model, including its components and the data it utilized, we cannot say that it erred in using the model in concluding that Velsi-col’s chemicals contaminated the plaintiffs’ wells as early as 1970. Next, Velsicol argues there was insufficient evidence to prove causation between plaintiffs’ ingestion, if any, of Velsicol’s chemicals and their alleged resultant injuries. The question of proximate cause is always to be determined on the facts of each ease. See Wooten v. United States, 574 F.Supp. 200 (W.D.Tenn.1982), aff'd, 722 F.2d 743 (6th Cir.1983); Ricker v. Zinser Textilmaschinen GmbH., 506 F.Supp. 3 (E.D.Tenn.1978), aff'd, 633 F.2d 218 (6th Cir.1980); Wyatt v. Winnebago Industries, 566 S.W.2d 276 (Tenn.App.1977); Mullins v. Seaboard Coastline Railway, 517 S.W.2d 198 (Tenn.App.1974); Carney v. Goodman, 38 Tenn.App. 55, 270 S.W.2d 572 (1954). On the basis of expert testimony (consisting of treating physicians, medical specialists, scientists, psychiatrists, clinical psychologists, engineers, hydrologists, and the plaintiffs themselves), numerous studies, and extensive literature, the district court concluded that Velsicol’s chemicals and the duration of the plaintiffs’ exposure to them were capable of causing the types of injuries alleged by the plaintiffs. The court also concluded that all of the five representative plaintiffs’ presently ascertainable and reasonably anticipated future injuries were proximately caused by ingesting or otherwise using the contaminated water. Thus, the court, as is appropriate in this type of mass tort class action litigation, divided its causation analysis into two parts. It was first established that Velsi-col was responsible for the contamination and that the particular contaminants were capable of producing injuries of the types allegedly suffered by the plaintiffs. Up to this point in the proceeding, the five representative plaintiffs were acting primarily in their representative capacity to the class as a whole. This enabled the court to determine a kind of generic causation — whether the combination of the chemical contaminants and the plaintiffs’ exposure to them had the capacity to cause the harm alleged. This still left the matter of individual proximate cause to be determined. Although such generic and individual causation may appear to be inextricably intertwined, the procedural device of the class action permitted the court initially to assess the defendant’s potential liability for its conduct without regard to the individual components of each plaintiff’s injuries. However, from this point forward, it became the responsibility of each individual plaintiff to show that his or her specific injuries or damages were proximately caused by ingestion or otherwise using the contaminated water. We cannot emphasize this point strongly enough because generalized proofs will not suffice to prove individual damages. The main problem on review stems from a failure to differentiate between the general and the particular. This is an understandably easy trap to fall into in mass tort litigation. Although many common issues of fact and law will be capable of resolution on a group basis, individual particularized damages still must be proved on an individual basis. To the extent that the plaintiffs seek damages for their bodily injuries, they must prove to a “reasonable medical certainty,” though they need not use that specific terminology, that their ingestion of the contaminated water caused each of their particular injuries. See Thompson v. Underwood, 407 F.2d 994 (6th Cir.1969); Maryland Casualty Co. v. Young, 211 Tenn. 1, 362 S.W.2d 241 (1962). This standard implicates the qualifications of the witnesses testifying, the acceptance in the scientific community of their theories, and the degree of certainty as to their conclusions. This standard is of particular importance when dealing with injuries or diseases of a type that may inflict society at random, often with no known specific origin. On numerous occasions, the Tennessee Supreme Court has addressed the degree of certainty of medical testimony required to establish a causal connection between a plaintiff’s injuries and a defendant’s tortious conduct. See e.g., Lindsey v. Miami Development Corp., 689 S.W.2d 856 (Tenn.1985); Owens Illinois, Inc. v. Lane, 576 S.W.2d 348 (Tenn.1978); P & L Construction Co. v. Lankford, 559 S.W.2d 793 (Tenn.1978); Laughlin Clinic, Inc. v. Henley, 208 Tenn. 252, 345 S.W.2d 675 (1961); Lynch v. LaRue, 198 Tenn. 101, 278 S.W.2d 85 (Tenn.1955). Whereas numerous jurisdictions have rejected medical experts’ conclusions based upon a “probability,” a “likelihood,” and an opinion that something is “more likely than not” as insufficient medical proof, the Tennessee courts have adopted a far less stringent standard of proof and have required only that the plaintiffs prove a causal connection between their injuries and the defendant’s tortious conduct by a preponderance of the evidence. While, in accordance with Tennessee common law, plaintiffs’ proof by a reasonable medical certainty requires them only to establish that their particular injuries more likely than not were caused by ingesting the contaminated water, their proofs may be neither speculative nor conjectural. Medical testimony that ingesting the contaminated water “possibly,” “may have,” “might have,” or “could have” caused the plaintiffs’ presently ascertainable or anticipated injuries does not constitute the same level of proof as a conclusion by a reasonable medical certainty. Although it is argued that a lesser standard of proof allocates loss on a socially acceptable basis, it is the province of the state legislatures to make such changes as they have done in some areas by establishing “no-fault” or other alternate systems. While upon review of the record in its entirety we cannot say that the district court abused its discretion in making its determination of the proximate causation between Velsicol’s chemical dumping operations, the resultant contamination of the plaintiffs’ water supply and the capacity of the contaminated water to cause the harms alleged, we find the district court erred in attributing all of the representative plaintiffs’ alleged injuries to drinking or otherwise using the contaminated water. We, therefore, address each category of the district court’s damage award. V. COMPENSATORY DAMAGES Velsicol argues that, even assuming proof of a proximate causation, the district court improperly awarded the five representative plaintiffs compensatory damages for their respective injuries and disabilities. The five representative plaintiffs, their exposure to Velsicol’s chemicals, and their respective injuries are as follows: Steven Sterling: Plaintiff Sterling, who was born December 25, 1922, in Hardeman County, Tennessee, utilized a well adjacent to his residence (Sterling well) for drinking purposes until November, 1977, and for all other purposes until November, 1978. During that time, he claimed to have drunk between ten and twelve glasses of the well water each day. He observed that, beginning in 1975, the well water developed a distinct odor, a bad taste, and contained an oily substance. Sterling testified that after ingesting, and otherwise using, the well water for a prolonged period of time, he suffered from headaches, nervousness, stomach and chest pains, shortness of breath, ringing in his ears, fatigue, loss of appetite and weight, nausea, coughing, vomiting, and peripheral neuropathy. Sterling further testified that he suffered from an enlarged liver with abnormal hepatic function, and an eighty percent reduction in his kidney function. Additionally, he developed emphysema in early 1976. Sterling was a heavy smoker for over forty-five years and previously worked in a cotton mill. James Wilbanks: Plaintiff Wilbanks, who was born in Walton, Mississippi, on June 15, 1931, lived in a mobile home with his family across from the Velsicol landfill from 1968 through 1971. During that time period, both Wilbanks and his family used water from a well adjacent to his property for drinking and bathing purposes (Tavern well). Beginning in 1971, Wilbanks commuted to work and used water at a tavern located across from the Velsicol landfill until it was closed and the well was capped in 1972. Thereafter, he used water obtained from two other wells for drinking and bathing purposes until 1978 (Sterling well and Rosetta Brooks well). Wilbanks testified that he suffered from headaches, dizziness, fatigue, nausea, vomiting, numbness, nervousness, ringing in his ears, shortness of breath, skin irritation, partial loss of eyesight including optic atrophy and neuritis, and peripheral neuropathy. Wil-banks lost his left kidney in 1981 due to cancer and suffers from emphysema. Curry Ivy: Plaintiff Ivy, who was born on January 3, 1926, in Chester County, Tennessee, drank contaminated water from three wells (Rosetta Brooks well, Velsicol Farm well, and Tavern well). He moved from the area in 1972. Ivy also was exposed to the ultrahazardous liquid and dry chemicals from January, 1972, through June, 1973, while he was employed by Vel-sicol to transport chemicals from its plant in Memphis, Tennessee, to its landfill in Hardeman County, Tennessee. Ivy testified that he suffered from headaches, dizziness, nausea, vomiting, nervousness, shortness of breath, fatigue, partial loss of eyesight including optic nerve neuritis and nerve dysfunction, and peripheral neuropa-thy. Ivy further testified that he suffered from liver and kidney damage and severe emphysema. Ivy’s medical history prior to drinking, or otherwise using, any contaminated well water included ulcers, stomach problems, severe emphysema, partial loss of vision, a heart attack, and various psychological problems. Ivy was a heavy smoker and previously worked in a cotton mill. Daniel Johnson: Plaintiff Johnson, who was born May 18, 1938, in Algoma, Mississippi, lived in Hardeman County from 1976 through 1978. During that time, Johnson and his family used water from a well adjacent to his property (Johnson well) for drinking and bathing purposes. Johnson testified that he suffered from headaches, loss of balance, fatigue, nausea, vomiting, numbness, nervousness, skin irritation, coughing, and partial loss of eyesight including optic nerve dysfunction. Johnson further testified that he suffered liver and kidney damage. Additionally, the Missouri Department of Health certified that, as of 1980, he was totally disabled and unable to continue employment as a result of psychological injuries. Johnson’s wife and daughter developed breast and uterus tumors. Mrs. Johnson previously suffered from fi-brocystic disease. James Maness, Jr.: Plaintiff Maness, who was born on September 1, 1976, drank and was bathed in water obtained from two wells (Sterling well and Mosier well) until approximately 1978. Additionally, while Maness’ mother was pregnant, she drank water obtained from the same wells. Maness allegedly suffered from frequent headaches, dizziness, nose bleeds, sore throat, nausea, and frequent vomiting. Additionally, Maness suffered from severe allergies, epilepsy, diabetes, blood discrasi-as, and an abnormally enlarged liver. Based upon these findings, the district court awarded the five representative plaintiffs compensatory damages for the following injuries: Sterling Wilbanks Ivy Johnson Maness Extent of Injury and Disability, Including Increased Risk of Cancer and Disease $ 150,000 $150,000 $ 75,000 $ 150,000 $ 250,000 Immune System Impairment 75,000 75,000 75,000 150,000 500,000 Post-Traumatic Stress Disorder 50,000 25,000 50,000 250,000 — Fear of Increased Risk of Cancer and Disease 75,000 100,000 50,000 250,000 250,000 Maness Sterling Wilbanks Ivy Johnson Physical Pain Emotional Suffering $ 125,000 $250,000 $ 50,000 $ 125,000 i — * Crc o © © Impaired Quality of Life 150,000 75,000 50,000 100,000 Or O © © © Real Property 48,492.50 — — — — Lost Wages Earning Capacity — — — 250,000 500,000 Learning Disorders — — — — 150,000 TOTAL: $673,492.50 $675,000 $350,000 $1,275,000 $2,300,000 A. Extent of Injury and Disability Velsicol asserts there was insufficient medical proof of the causal connection between ingestion of contaminated water and certain injuries. First, we focus upon that portion of the award attributed to the plaintiffs’ actual physical injuries and then upon the portion of the award attributed to their increased susceptibility to cancer and other diseases. 1. Presently Ascertainable Injuries As a portion of its award for the extent of their injuries and disabilities proximately caused by ingesting the contaminated water, the district court awarded the five representative plaintiffs damages for their presently ascertainable injuries. In its opinion and order granting judgment to the plaintiffs, with respect to plaintiffs Sterling, Johnson, and Maness, the district court merely referred to the “extent of [their] injury and disability” without further indicating which specific injuries were included in this category. However, the district court clarified the basis of its award by adopting and incorporating into its opinion findings of fact submitted by the plaintiffs’ counsel. By adopting such findings, the court credited plaintiffs’ evidence that plaintiffs Sterling, Johnson, and Maness each suffered from kidney and liver damage and numerous central nervous system injuries. In its opinion and order with respect to plaintiff Wilbanks, the court referenced the “loss of one kidney already to cancer and optic atrophy and neuritis” as some of the elements of its award and, with respect to plaintiff Ivy, the court referenced “optic atrophy and neuritis” as some of the elements of its award. The court further adopted the plaintiffs’ proposed findings to the effect that plaintiffs Wilbanks and Ivy also suffered from kidney and liver damage and numerous central nervous system injuries. In seeking damages for actual physical injuries, a plaintiff must prove to a reasonable medical certainty that his or her injuries were caused by a defendant’s acts or omissions. To this extent, an award is not insulated from review merely because the trial court refrains from particularizing the basis of a general injury award. If, for example, a plaintiff fails to establish sufficient causation between a defendant’s acts and a specific injury, we may, nonetheless, remand the entire award to exclude that portion of the award, if any, attributed to that specific injury for which proof is lacking. Velsicol specifically avers that the plaintiffs failed to prove to a reasonable medical certainty that Wilbanks’ kidney cancer, all of the plaintiffs’ loss of kidney and liver functions and central nervous system injuries, and Wilbanks’ and Ivy’s optic atrophy and neuritis were caused by ingesting contaminated water. With respect to Wilbanks’ kidney cancer, plaintiffs’ testifying physician, Dr. Rhamy, stated that “based upon a reasonable medical certainty ... its more likely [that Wilbanks’ kidney cancer] was caused by the chemicals.... ” While Dr. Rhamy conceded that “[n]o one knows what causes cancer of the kidney,” his testimony that Wilbanks’ environmental exposure to carbon tetrachloride was the reasonable and probable cause for his kidney cancer constitutes sufficient medical proof. The plaintiffs’ testifying physicians, Drs. Balistreri, Clark, Rhamy, and Rodricks, further testified to a reasonable medical certainty that each of the plaintiff’s loss of kidney and liver functions and central nervous system disorders were caused by their exposure to the contaminated water. However, the plaintiffs failed to prove to a reasonable medical certainty that either Wilbanks’ or Ivy’s optic atrophy and neuritis were caused by ingesting or otherwise using the contaminated water. While plaintiffs’ own expert neuroopthamologist, Dr. Drewery, stated that Ivy’s eye problems and his exposure to carbon tetrachloride were causally related and that his reduction in visual acuity and visual field were compatible with toxic exposure, Dr. Drewery, based upon his own tests, concluded that Ivy did not have optic atrophy. Indeed, no physician diagnosed Ivy as suffering from optic atrophy. Dr. Drewery’s statement that he was unable to “uncover any ... other medically probable explanation for Mr. Ivy’s visual problems than chemical exposure,” when considered in view of his negative diagnosis, and Dr. Rhamy’s observation that Ivy had a paleness of the optic disc (which Dr. Drewery did not observe) does not constitute sufficient medical proof. Similarly, no physician diagnosed or testified to a reasonable medical certainty that Wilbanks’ visual difficulties were caused by his exposure to contaminated water. While plaintiffs Johnson’s, Maness’, and Sterling’s presently ascertainable injuries were all sufficiently substantiated by competent medical testimony, the district court’s award to plaintiffs Wilbanks and Ivy is remanded for recalculation to exclude that portion of the award attributed to the specific injuries we have found to be unsupported by sufficient medical proof. 2. Increased Risk of Cancer and Other Diseases Plaintiffs sought to recover damages for the prospect that cancer and other diseases may materialize as a result of their exposure. The district court awarded the five representative plaintiffs damages predicated upon their being at risk for, or susceptible to, future disease. Where the basis for awarding damages is the potential risk of susceptibility to future disease, the predicted future disease must be medically reasonably certain to follow from the existing present injury. While it is unnecessary that the medical evidence conclusively establish with absolute certainty that the future disease or condition will occur, mere conjecture or even possibility does not justify the court awarding damages for a future disability which may never materialize. Tennessee law requires that the plaintiff prove there is a reasonable medical certainty that the anticipated harm will result in order to recover for a future injury. See Thompson v. Underwood, 407 F.2d 994 (6th Cir.1969); Maryland Casualty Co. v. Young, 211 Tenn. 1, 362 S.W.2d 241 (1962); see also Shelton v. College Station, 765 F.2d 456 (5th Cir.1985). Therefore, the mere increased risk of a future disease or condition resulting from an initial injury is not compensable. While neither the Tennessee courts, nor this court, has specifically addressed damage awards for increased risk or susceptibility to cancer and kidney and liver diseases, numerous courts have denied recovery where plaintiffs alleged they might suffer from these future diseases or conditions as a result of existing injuries. For example, in Ayers v. Jackson, 189 N.J. Super. 561, 461 A.2d 184 (1983), 325 county residents alleged that toxic wastes leaked through the municipal landfill and contaminated their well water. Plaintiffs’ experts testified the ground water was contaminated with numerous known carcinogenic chemicals including benzene, acetone, and chloroform. Plaintiffs argued they suffered from a present condition of enhanced risk of kidney and liver disease and cancer from ingesting the contaminated well water. The Ayers court held that damages were not recoverable for such prospective consequences where the plaintiffs’ proofs did not establish that they would in the future, to a reasonable medical certainty, suffer from such injury. The court observed that all individuals who were exposed to the well water contamination were at an increased risk of developing cancer and liver and kidney damage. However,; the court noted that because plaintiffs’ experts could not formulate a quantitative measure to a reasonable medical certainty of excess kidney, liver, and cancer risk, it was left to speculation as to possible consequences of the ingestion of the alleged carcinogens on the future health of each plaintiff. Similarly, in Hagerty v. L & L Marine Services, Inc., 788 F.2d 315 (5th Cir.), reconsideration denied, 797 F.2d 256 (5th Cir.1986) (en banc), a plaintiff who was accidentally drenched with chemcials containing known carcinogens, sued for damages including compensation for the increased risk that he would develop cancer in the future as a result of his exposure. The court concluded that because he did not allege with medical certainty that he would develop cancer in the future, he did not state a claim. The court reasoned that plaintiff’s increased risk of cancer was not presently compensable because he could not show that the toxic exposure would more probably than not lead to cancer. See also Herber v. Johns-Manville Sales Corp., 785 F.2d 79 (3d Cir.1986); Devlin v. Johns-Manville Sales Corp., 202 N.J.Super. 556, 495 A.2d 495 (1985) (plaintiffs’ claims for enhanced risk of cancer from asbestos exposure denied where plaintiffs' expert unable to state to a reasonable medical certainty that plaintiffs would get cancer in the future); Briggs v. New York Central Hudson River Railroad, 177 N.Y. 59, 69 N.E. 223 (1903) (kidney problems resulting from spinal injury found to be conjectural and speculative and not a basis of award for damages). In the instant case, the district court found an increased risk for susceptibility to cancer and other diseases of only twenty-five to thirty percent. This does not constitute a reasonable medical certainty, but rather a mere possibility or speculation. Indeed, no expert witnesses ever testified during the course of trial that the five representative plaintiffs had even a probability — i.e., more than a fifty percent chance — of developing cancer and kidney or liver disease as a result of their exposure to defendant’s chemicals. For the foregoing reasons, the district court’s award of compensatory damages to each of the five representative plaintiffs is remanded for recalculation to exclude that portion of the damage award attributed to increased susceptibility to cancer and other diseases. B. Fear of Increased Risk of Cancer and Other Diseases Yelsicol next argues that the district court erroneously awarded the five representative plaintiffs compensatory damages or, in the alternative, excessive damages for fear of increased risk of contracting cancer and other diseases. Mental distress, which results from fear that an already existent injury will lead to the future onset of an as yet unrealized disease, constitutes an element of recovery only where such distress is either foreseeable or is a natural consequence of, or reasonably expected to flow from, the present injury. See Payton v. Abbott Labs, 386 Mass. 540, 437 N.E.2d 171 (1982); Ferrara v. Galluchio, 5 N.Y.2d 16, 152 N.E.2d 249, reh’g denied, 5 N.Y.2d 793, 180 N.Y.S.2d 1025, 154 N.E.2d 581 (1958); Jones v. United Railroads of San Francisco, 54 Cal.App. 744, 202 P. 919 (1921). However, damages for mental distress generally are not recoverable where the connection between the anxiety and the existing injury is either too remote or tenuous. See, e.g., Howard v. Mt. Sinai Hospital, 63 Wis.2d 515, 217 N.W.2d 383 (1974). While there must be a reasonable connection between the injured plaintiffs mental anguish and the prediction of a future disease, the central focus of a court’s inquiry in such a case is not on the underlying odds that the future disease will in fact materialize. To this extent, mental anguish resulting from the chance that an existing injury will lead to the materialization of a future disease may be an element of recovery even though the underlying future prospect for susceptibility to a future disease is not, in and of itself, compensable inasmuch as it is not sufficiently likely to occur. In the context of certain types of injuries and exposures to certain chemicals, cancerphobia has been one basis of claims for mental anguish damages. In Tennessee, damages for fear arising from an increased risk of disease are recoverable. Laxton v. Orkin Exterminating Co., 639 S.W.2d 431 (Tenn.1982). In Lax-ton, the plaintiffs’ water supply was contaminated by the carcinogens chlordane and heptachlor when defendant serviceman sprayed the exterior of plaintiffs’ house for termites. The Department of Water Quality Control told plaintiffs to cease using the water for any purpose and to obtain a new water source. As a result of ingesting the contaminated water for over a period of eight months, the plaintiffs worried about their health and the health of their children. The court awarded the plaintiffs $6,000 each for their mental suffering resulting from their reasonable apprehension of the harmful effects to their own and their children’s health due to consuming or otherwise using the contaminated water. The Laxton court noted that the period of “mental anguish” deserving compensation was confined to the time between the discovery of ingestion of toxic substances and the determination that puts to rest the fear of future injury. In the instant case, the plaintiffs’ fear clearly constitutes a present injury. Each plaintiff produced evidence that they personally suffered from a reasonable fear of contracting cancer or some other disease in the future as a result of ingesting Velsicol’s chemicals. Consistent with the extensive line of authority in both Tennessee and other jurisdictions, we cannot say that the district court erred in awarding the five representative plaintiffs damages for their reasonable fear of increased risk of cancer and other diseases. In the alternative, Velsicol asserts that the district court awarded excessive damages to the plaintiffs. The amount of the damage award in a personal injury action is for the jury or, in a non-jury case, the trial judge who heard the evidence. Absent a showing of bias, passion, or corruption, excessiveness of a verdict is left to the trial court’s discretion. The appellate court will only consider whether the trial court abused that discretion by granting awards so large as to shock the judicial conscience. See Stengel v. Belcher, 522 F.2d 438 (6th Cir.1975), cert. dismissed, 429 U.S. 118, 97 S.Ct. 514, 50 L.Ed.2d 269 (1976); Kroger Co. v. Rawlings, 251 F.2d 943 (6th Cir.1958); Olson v. Sharpe, 36 Tenn.App. 557, 259 S.W.2d 867, cert. denied, Tenn.S.Ct. (1953); Yellow Cab Co. v. Pewitt, 44 Tenn.App. 572, 316 S.W.2d 17, cert. denied, Tenn.S.Ct. (1958). When considering whether an award is so excessive, this court considers other awards in other cases, as well as the nature and extent of the injuries. Martin v. Southern Railway, 225 Tenn. 77, 463 S.W.2d 690 (1971); France v. Newman, 35 Tenn.App. 486, 248 S.W.2d 392 (1951), cert. denied, Tenn.S.Ct. (1952). The evidence credited by the court shows that each of the plaintiffs suffered from, and should be compensated for, a reasonable fear of contracting cancer or some other diseases in the future. The only issue is the amount of reasonable compensation. In Laxton, the court limited the amounts of recovery to $6,000 for each plaintiffs reasonable fear of future disease from ingesting known carcinogens over an extended period of time. In the instant case, the district court awarded plaintiffs damages ranging from $50,000 to $250,000. We find these awards to be excessive, particularly where plaintiffs failed to prove at trial that they have a significant increased risk of contracting cancer and other diseases. Upon a review of the opinion and the adopted findings of fact, we are unable to find any basis upon which the district court differentiated its damage awards to each plaintiff for his or her fear of increased risk of cancer and other diseases. The Laxton court awarded each plaintiff $6,000 for his or her fear of increased susceptibility to cancer from consuming known carcinogens for a duration of eight months. Using Laxton as a guidepost, we, accordingly, vacate the district court’s award and award each of the five representative plaintiffs damages based upon the duration of their exposure to the contaminated water. Plaintiff Johnson, who was exposed to the chemicals for a period of approximately two years, is awarded $18,000 versus the district court’s award of $250,000; plaintiff Maness, who was exposed for approximately three years (two years during infancy and approximately one year while his mother was exposed to the chemicals during pregnancy), is awarded $27,000 versus the district court’s award of $250,000; plaintiff Ivy, who was exposed for approximately four years, is awarded $36,000 versus the district court’s award of $50,000; plaintiff Wilbanks, who was exposed for approximately six years, is awarded $54,000 versus the district court’s award of $100,000; and plaintiff Sterling, who was exposed for approximately eight years, is awarded $72,000 versus the district court’s award of $75,000. C. Immune System Impairment and Learning Disorders Velsicol argues that the district court erroneously awarded all of the plaintiffs damages for alleged impairment to their immune systems and to plaintiff Maness for his additional learning disorders due to his immune system impairment. Velsicol specifically alleges that the court improperly admitted and relied upon testimony which purported to show Velsicol’s chemicals harmed plaintiffs’ immune systems because the principles upon which the experts based their conclusions were not in conformity to a generally accepted explanatory theory. The admissibility of expert testimony is governed by Fed.R.Evid. 702 which provides: If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise. In accordance with Rule 702, a four-part test must be met to uphold the admission of “expert testimony”: (1) a qualified expert (2) testifying on a proper subject (3) which is in conformity to a generally accepted explanatory theory (4) the probative value of which outweighs its prejudicial effect. United States v. Kozminski, 821 F.2d 1186, 1194 (6th Cir.), cert. granted on other grounds, — U.S. -, 108 S.Ct. 225, 98 L.Ed.2d 185 (1987); United States v. Brown, 557 F.2d 541 (6th Cir.1977); United States v. Green, 548 F.2d 1261 (6th Cir.1977). With respect to the third criterion, the principles upon which the scientific evidence is based must be sufficiently established to have gained wide acceptance in the field to which it belongs. As we reasoned in United States v. Brown: There are good reasons why not every ostensibly scientific technique should be recognized as the basis for expert testimony. Because of its apparent objectivity, an opinion that claims a scientific basis is apt to carry undue weight with the trier of fact. In addition, it is difficult to rebut such an opinion except by other experts or by cross-examination based on a thorough acquaintance with the underlying principles. In order to prevent deception or mistake and to allow the possibility of effective response, there must be a demonstrable, objective procedure for reaching the opinion and qualified persons who can either duplicate the result or criticize the means by which it was reached, drawing their own conclusions from the underlying facts. 557 F.2d at 556, quoting United States v. Baller, 519 F.2d 463, 466 (4th Cir.), cert. denied, 423 U.S. 1019, 96 S.Ct. 456, 46 L.Ed.2d 391 (1975). A review of the record reveals that plaintiffs failed to meet the third criterion of the test. Plaintiffs’ testifying expert immunologist, Dr. Levin, and testifying pediatrician, Dr. Crook, stated that, on the basis of clinical ecological tests, Velsicol’s chemicals damaged plaintiffs’ immune systems. Clinical ecology is premised on a belief that exposure to a number of factors including, but not limited to, anxiety, radiation, certain chemicals, and even some common household substances can cause dysregulation of the immune system. Treatment for immune system dysregulation consists of rigid diet and environmental control. The leading professional societies in the specialty of allergy and immunology, the American Academy of Allergy and Immunology (AAAI) and the California Medical Association (CMA), have rejected clinical ecology as an unproven methodology lacking any scientific basis in either fact or theory. According to the AAAI, “[t]he theoretical basis for ecologic illness in the present context has not been established as factual, nor is there satisfactory evidence to support the actual existence of ‘immune system dysregulation’ or maladaption.” Position Statements: Clinical Ecology, 78 J. Allergy Clinical Immunology, 269, 270 (Aug. 1986). The CMA concludes that there is “[n]o convincing evidence ... that the diagnostic tests employed are efficacious and reliable or that the treatments used are effective.” Clinical Ecology—A Critical Appraisal, W.J. of Med., 239, 243 (Feb. 1986). While numerous other professional organizations and societies, such as the American Medical Association, the American Board of Allergy and Immunology, and the American Academy of Otolar-yngic Allergy, have not discredited completely the potential usefulness of clinical ecology, few have endorsed either its scientific methodology or the results of any experiments conducted under the guise of clinical ecology. Indeed, plaintiffs’ experts neither performed nor could identify any studies of the effects of carbon tetrachloride or chloroform on the immune system. In reaching their conclusions of immune system dysregulation, plaintiffs’ experts neither personally examined or interviewed plaintiffs, nor performed the requisite medical tests. The experts based their opinions upon certain blood tests, which revealed a higher than normal white blood cell count, and the plaintiffs’ medical histories supplied by their attorneys. Without the requisite clinical tests and a widely accepted medical basis for reaching its conclusions, plaintiffs’ experts’ opinions are insufficient to sustain plaintiffs’ burden of proof that the contaminated water damaged their immune system. The record reveals that plaintiff Maness was borderline retarded and suffered from a severe learning disorder. The sole evidence allegedly linking Maness’ learning problems to his chemical exposure was offered by clinical ecologist, Dr. Crook. Dr. Crook testified that Maness’ and his mother’s ingestion of toxic chemicals “so compromised his resistance that it set him up for a variety of health problems” — in essence immune system dysregulation. Dr. Crook based his conclusions on two examinations in which he determined Maness’ physical condition was normal and Maness’ general medical history which was provided by his grandmother. He performed no scientific tests to determine the source of Maness’ learning disorder. Despite the testimony of other physicians which attributed Maness’ learning disorder to other factors, Dr. Crook dismissed the evidence reasoning that “those physicians are unaware of the role of chemical sensitivity in triggering health problems ... I feel I have knowledge of [Maness] that they don’t have.” Despite his personal speculations, Dr. Crook provided no medical basis justifying his conclusion that Maness’ learning disorder was caused by ingesting or otherwise using the contaminated water. Accordingly, we reverse the district court’s award of damages to all of the plaintiffs for immune system impairment and to plaintiff Maness for his learning disorder arising out of impairment to his immune system. D. Post-Traumatic Stress Disorder Velsicol argues that the district court improperly awarded four of the five representative plaintiffs damages for post-trau