Quiz 1, Module Bias
1. Investigators recruited both cases and controls from a defined catchment area in the general population. This is often difficult to do in the absence of a comprehensive case registry. Suppose that investigators had recruited all cases of breast cancer from a comprehensive national registry, between August 1, 1996 and July 31, 1997. What type of bias might be introduced if investigators kept the same set of controls as were reported in the Teitelbaum et al. (2007) study?
Answer (a) —
correct:
The control group should represent the exposure probability of the source population that gave rise to the cases (note: exposure probability does not mean the same as probability of exposure in cases and controls; instead, it refers to the exposure probability of the underlying source population of non-cases that gave rise to the cases). Given that the national registry includes cases from across the U.S., it makes defining our source population somewhat tricky. Since controls in this scenario were obtained from the general population of Nassau and Suffolk counties, it is certain that the controls and cases came from different geographic areas. This creates the potential for selection bias since cases and controls did not come from the same source population. Moreover, the controls may systematically differ from the cases in many important ways that are related to the exposure. Resident of Nassau and Suffolk counties have, on average, a higher socio-economic status than most counties in the U.S. If, controls were of a higher SES than cases in the national registry, and SES is believed to be related to both the exposure (lawn/garden pesticide use) and the disease outcome (breast cancer), this could bias the association.
Answer (b) —
incorrect:
This has nothing to do with recall bias because recall bias is a type of information bias. The problem in this situation is not with obtaining information from cases and controls but with selecting cases and controls.
Answer (c) —
incorrect:
Case-control studies with low to moderate participation rates are susceptible to self-selection bias arising from: (1) refusal or non-response by participants that is related to both the exposure and the disease, or (2) agreement to participate that is related to both the exposure and disease occurring when participation rates between cases and controls differ in a way that is linked to the exposure (Aschengrau & Seage, p. 266). While self-selection bias may be operating in this situation, the scenario given in the question refers to a different type of bias.
