Epidemiology is the field of public health and medicine that studies the incidence, distribution, and etiology of disease in human populations. The purpose of epidemiology is to better understand disease causation and to prevent disease in groups of individuals. Epidemiology assumes that disease is not distributed randomly in a group of individuals and that identifiable subgroups, including those exposed to certain agents, are at increased risk of contracting particular diseases.1
Judges and juries are regularly presented with epidemiologic evidence as the basis of an expert’s opinion on causation.2 In the courtroom, epidemiologic research findings are offered to establish or dispute whether exposure to an agent3
1. Although epidemiologists may conduct studies of beneficial agents that prevent or cure disease or other medical conditions, this reference guide refers exclusively to outcomes as diseases, because they are the relevant outcomes in most judicial proceedings in which epidemiology is involved.
2. Epidemiologic studies have been well received by courts deciding cases involving toxic substances. See, e.g., Siharath v. Sandoz Pharms. Corp., 131 F. Supp. 2d 1347, 1356 (N.D. Ga. 2001) (“The existence of relevant epidemiologic studies can be a significant factor in proving general causation in toxic tort cases. Indeed, epidemiologic studies provide ‘the primary generally accepted methodology for demonstrating a causal relation between a chemical compound and a set of symptoms or disease.’” (quoting Conde v. Velsicol Chem. Corp., 804 F. Supp. 972, 1025–26 (S.D. Ohio 1992))), aff’d, 295 F.3d 1194 (11th Cir. 2002); Berry v. CSX Transp., Inc., 709 So. 2d 552, 569 (Fla. Dist. Ct. App. 1998). Well-conducted studies are uniformly admitted. 3 Modern Scientific Evidence: The Law and Science of Expert Testimony § 23.1, at 187 (David L. Faigman et al. eds., 2007–08) [hereinafter Modern Scientific Evidence]. Since Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993), the predominant use of epidemiologic studies is in connection with motions to exclude the testimony of expert witnesses. Cases deciding such motions routinely address epidemiology and its implications for the admissibility of expert testimony on causation. Often it is not the investigator who conducted the study who is serving as an expert witness in a case in which the study bears on causation. See, e.g., Kennedy v. Collagen Corp., 161 F.3d 1226 (9th Cir. 1998) (physician is permitted to testify about causation); DeLuca v. Merrell Dow Pharms., Inc., 911 F.2d 941, 953 (3d Cir. 1990) (a pediatric pharmacologist expert’s credentials are sufficient pursuant to Fed. R. Evid. 702 to interpret epidemiologic studies and render an opinion based thereon); Medalen v. Tiger Drylac U.S.A., Inc., 269 F. Supp. 2d 1118, 1129 (D. Minn. 2003) (holding toxicologist could testify to general causation but not specific causation); Burton v. R.J. Reynolds Tobacco Co., 181 F. Supp. 2d 1256, 1267 (D. Kan. 2002) (a vascular surgeon was permitted to testify to general causation); Landrigan v. Celotex Corp., 605 A.2d 1079, 1088 (N.J. 1992) (an epidemiologist was permitted to testify to both general causation and specific causation); Trach v. Fellin, 817 A.2d 1102, 1117–18 (Pa. Super. Ct. 2003) (an expert who was a toxicologist and pathologist was permitted to testify to general and specific causation).
3. We use the term “agent” to refer to any substance external to the human body that potentially causes disease or other health effects. Thus, drugs, devices, chemicals, radiation, and minerals (e.g., asbestos) are all agents whose toxicity an epidemiologist might explore. A single agent or a number of independent agents may cause disease, or the combined presence of two or more agents may be necessary for the development of the disease. Epidemiologists also conduct studies of individual characteristics, such as blood pressure and diet, which might pose risks, but those studies are rarely of interest in judicial proceedings. Epidemiologists also may conduct studies of drugs and other pharmaceutical products to assess their efficacy and safety.