For each of the following, choose the option that applies to case-control studies:


a. The investigator's role regarding exposure:
A assign B observe

b. Subject selection into groups:
A self-selection B randomization

d. Directionality:
A backwards B forwards C non-directional

e. Timing:
A prospective B retrospective C either

e. Analysis by:
A original assignment B actual experience

a. The investigator's role regarding exposure:

In case-control studies, the investigator observes the exposure of the cases and controls. Therefore, the option that applies is B - observe.

b. Subject selection into groups:
In case-control studies, the selection of subjects into groups is not randomized. Instead, the cases and controls are selected based on their disease status. Therefore, the option that applies is A - self-selection.

c. Directionality:
Case-control studies are generally non-directional, meaning they do not establish a temporal relationship between exposure and disease. Therefore, the option that applies is C - non-directional.

d. Timing:
Case-control studies can be either prospective or retrospective. Prospective case-control studies identify cases as they occur and select controls from the defined population at the outset. Retrospective case-control studies identify cases that have already occurred and select controls based on the same population from which the cases arose. Therefore, the option that applies is C - either.

e. Analysis by:
In case-control studies, the analysis is typically done by comparing the original assignment of exposure (i.e., the way exposure was measured or assigned at the time of the study) between cases and controls. Therefore, the option that applies is A - original assignment.