Certified in Public Health (CPH) Practice Exam

In cohort studies regarding a suspected factor's role in disease, what must be ensured at the study's initiation?

1. Subjects should have equal numbers in both groups.

2. Those with and without the disease must have equal risks of exposure to the factor.

3. Both study groups should be similar concerning potential confounders.

4. The disease incidence must be high.

The correct answer is: Both study groups should be similar concerning potential confounders.

In cohort studies, it is essential to ensure that both study groups are similar concerning potential confounders at the study's initiation. This similarity allows for a more accurate assessment of the relationship between the suspected factor and the disease. Confounders are variables that may influence both the exposure and the outcome, leading to spurious associations if not controlled. By ensuring the groups are comparable with regard to these confounding factors, researchers can more confidently attribute any differences in disease incidence to the exposure of interest rather than to these other variables. For instance, if one group has a higher socioeconomic status and different access to healthcare compared to another group, any observed differences in disease incidence could be due to these factors rather than the exposure being studied. Thus, controlling for confounders is crucial in establishing a valid causal relationship between exposure and outcome. While having equal numbers in both groups (the first choice) might help with statistical power, it does not address the essence of confounding. Similarly, equal risks of exposure (the second choice) is not a requirement, as cohort studies can still compare different exposure levels between groups. Lastly, high disease incidence (the fourth choice) is not a prerequisite for a cohort study and may even be undesirable in cases where the disease is