An Investigator Tests 100 Children at the Beginning of a Longitudinal

An investigator tests 100 children at the beginning of a longitudinal study and then follows up on his subjects, testing the 50 he can locate 5 years later. The fact that only half the original sample can now be located is a(n) _____ because _____.

A) advantage; the possibility of cohort effects is lessened
B) advantage; the research costs less to complete
C) disadvantage; the study is subject to cross-generational problems
D) disadvantage; any conclusions drawn may be based on a non?-representative sample