Describe some problems that investigators face in conducting longitudinal research

What will be an ideal response?

Answer: Despite their strengths, longitudinal investigations pose a number of problems. For example, biased sampling—the failure to enlist participants who adequately represent the population of interest—is a common problem. People who willingly participate in research that requires them to be observed and tested over many years are likely to have distinctive characteristics, such as a special appreciation for the scientific value of research. Furthermore, longitudinal samples generally become more biased as the investigation proceeds because of selective attrition. Participants may move away or drop out of the study for other reasons, and the ones who remain are likely to differ in important ways from the ones who do not continue. Also, from repeated study, people may become "test-wise." Their performance may improve as a result of practice effects—better test-taking skills and increased familiarity with the test—not because of factors commonly associated with development. Finally, the most widely discussed threat to the accuracy of longitudinal findings is cultural–historical change, commonly called cohort effects. Longitudinal studies examine the development of cohorts—children born at the same time, who are influenced by particular cultural and historical conditions. Results based on one cohort may not apply to children developing at other times.