Occupational Epidemiology: Some Guideposts
Authors: Gamble John F. 
Published: August 2005

Abstract
It is the nature of modern human beings to speculate on the causes of disease. Often this speculation centers on factors associated with work, and the recognition of disease‐producing agents in occupational settings has resulted in striking health improvements in some groups of workers. Such conditions as lead intoxication, mercury poisoning, and benzol poisoning have largely disappeared because they could be easily identified with a particular substance, and industrial hygiene measures were relatively easy to apply. For some occupational disease, such as bladder cancer in the dye industry and phossy jaw in the match industry, the use of certain substances was simply stopped in order to protect the health of the worker.
As the more obvious industrial hazards have been identified and brought under control, the task of identifying disease produced by occupational exposure has become increasingly difficult. In many instances environmental or occupational exposures may be low so that our ability to distinguish response from background is limited. Nevertheless, studying human populations to assess the determinants of disease has several advantages over other methods. In particular, humans comprise the population of interest, and they are studied in the real world where the exposure actually occurs.
Epidemiology may be defined as the study of health and illness in human populations. It is the study of the distribution of determinants of health‐related states and events in populations, and the application of this study to the control of health problems. It is a method of reasoning about disease that deals with biological inferences derived from observations of disease phenomenon in population groups.
Although epidemiologists do not always agree on a definition of epidemiology, or on the scope of activities included in this scientific discipline, there are features of epidemiology that can serve to characterize it as a field of study. The statements listed below should help to orient one as to what epidemiology is about.

Contrasts experimental research and epidemiological research, which is observational in nature. The form and presentation of results in an experimental animal study or clinical trial appear to be similar in the comparison of exposed and control groups. However, the experimental study has control over study subjects and exposures, while the epidemiology study is observational and cannot determine
a priori
the composition of the study population or the intensity and duration of exposure. The study designs that are unique to epidemiology are discussed with consideration of their strengths and weaknesses. They differ fundamentally from experimental research in that cause–effect cannot be assumed, even if the results are statistically significant.

The observational nature of epidemiology means that one must always be wary of biases that can lead to spurious interpretations. Descriptions of studies will be presented to help explain the concepts presented and provide examples of the kind of skeptical consideration required to find a true cause. Or to avoid the “wish bias,” the tendency to make causal conclusions (or not) on the basis of an inherent tendency to “wish for” a desired result.