Designing and Conducting Analytic Studies in the Field

Analytic studies enable the field epidemiologist to test his or her hypotheses about the source of an outbreak or other health problem. This testing is performed by comparing ill persons’ exposures to those of a comparison group, typically using one of three study types. Cohort studies are used in field investigations when the population affected is well defined and not so large as to preclude collecting data on almost all persons. Case–control studies are commonly used in field investigations because they enable investigators to test multiple hypotheses relatively quickly and inexpensively. Case–case studies, in which the comparison group comprises other patients with the same or similar illness who do not meet the case definition also can be used to rapidly test hypotheses. Although field investigations may be conducted under intense scrutiny and time pressure, be sure to take time to develop hypotheses and carefully design any study.