Describe the problems in conducting longitudinal research

What will be an ideal response?

Longitudinal investigations pose a number of problems that can compromise both internal and external validity. Difficulties include:
– Biased sampling: The failure to enlist participants who represent the population of interest is a common difficulty. 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, or a unique need or desire for medical, mental health, or educational services provided by the investigators. As a result, researchers cannot easily generalize from them to the rest of the population.
– Selective attrition: Participants may move away or drop out for other reasons, and those who continue are likely to differ in important ways from those who drop out.
– Practice effects: With repeated testing, participants may become "test-wise." Their performance may improve as a result of better test-taking skills and increased familiarity with the test, not because of factors commonly associated with development. The very experience of being repeatedly observed, interviewed, and tested can also interfere with a study's validity. As children and adults are alerted to their own thoughts, feelings, and actions, they may consciously revise them in ways that have little to do with age-related change.
– Cohort effects: Longitudinal studies examine the development of cohorts—children developing in the same time period who are influenced by particular cultural and historical conditions. Results based on one cohort may not apply to children developing at other times. Cohort effects don't just operate broadly on an entire generation. They also occur when specific experiences influence some children but not others in the same generation.
– Outdated theory and methods: Changes occurring within the field of child development may create problems for longitudinal research covering an extended time period. Theories and methods that first inspired a longitudinal study may become outdated.