The strategy which is not aimed at reducing selection bias is:

A. Development of an explicit definition for cases and controls
B. Standardization of study procedures
C. Enrollment of cases from settings where the exposure is expected to be higher than the general population
D. None of the above.

D.

Explanation:

A Selection Bias can be defined as an experimental bias that occurs in the process of selection of participants. This bias avoids the random selection of the participants thus creates a problem in the research study as the results will not represent the target audience. Selection bias occurs due to many reasons but self-selection is prevalent.

To reduce the possibilities of selection bias, several strategies are adopted. Several of them are stated in options, that is standardization, enrollment, and development of an explicit definition. Other strategies include randomization.

So, from the given options, the correct one is D because all others are strategies for reducing selection bias.