"Attrition" is a reduction in the number of research participants as some drop out of the study over time.
Attrition is a term used to depict a rate of decrease after some time. For instance, representative attrition in the work environment alludes to the rate at which workers quit or leave to take different occupations. In psychological studies, selective attrition depicts the propensity of a few people to probably drop out of an examination than others.