confounding (i.e., misattribution of cause [Greenland, 1989, 1992; Richardson et al., 1987; Rothman, 1990; Susser, 1994a,b]).

Although many of the preepidemiologic approaches make clever use of scant data, some scientists question the reliability and utility of such analyses (Neutra, 1990; Rothman, 1990). Because the limitations of each specific data set define its interpretableness and generalizability, these limitations must be made explicit both to researchers and to the community under study. This includes discussions with the community about the limitations of the methods before any data collection or data analyses are undertaken, lest false expectations be raised.

On the other hand, preepidemiologic studies of case reports can be extremely useful as screening tools and for guidance in epidemiologic design. For example, in the 1850s, John Snow, a British physician, noticed higher death rates from cholera in one area of London than another. He hypothesized that this might be due to the source of the drinking water and its proximity to sewage disposal areas. By preventing access to the suspected contaminated water supply by removing the water pump handle, Snow was able to confirm his hypothesis (Snow, 1965).

Similarly, in Woburn, Massachusetts, in the early 1980s, residents reported excess cases of childhood leukemia that were confirmed by preepidemiologic analyses. A rigorous epidemiologic study further validated the residents' concerns and implicated chemically contaminated drinking water as the cause (Lagakos et al., 1986). The results of the latter study remain controversial, although a recent report supports the initial finding of cases of excess disease and reports a subsequent decline after appropriate allowance for latency.

In 1971, Herbst and coworkers reported on eight cases of adenocarcinoma of the vagina in women aged 15 to 22 in Massachusetts in which diethylstilbestrol was implicated as the disease-causing agent (Herbst et al., 1971). A year later, the observation of three cases of angiosarcoma of the liver among polyvinyl chloride production workers was used to implicate the vinyl chloride monomer as a cause of disease in a worker population (Creech and Johnson, 1974). Another workplace cluster of disease, male infertility in the pesticide industry, was used to identify the manufacture of dibromochloropropane as dangerous (Whorton et al., 1977). Several cases of phocomelia alerted experts to the problems of thalidomide. The identification of risk factors for human immunodeficiency virus transmission and AIDS also arose out of case reports from preepidemiologic studies (Centers for Disease Control, 1981). Finally, studies of soybeans and asthma attacks have identified soybeans as a new etiologic factor for the disease, and studies of Hodgkin's disease in young adults and mesothelioma in the small village of Karain, Turkey, have helped focus further epidemiologic studies that eventually led to a reduction in the number of cases of disease (Alexander, 1992). In short, although many question the utility of these