A problem with cross-sectional research is that cohort ...

[joblessjake]

A problem with cross-sectional research is that
 
  cohort differences can make it difficult to differentiate between developmental
  change and cohort differences.
  retesting leads older subjects to do better.
  the most intelligent people are most likely to drop out of the study.
  the results tend not to be worth the large investment.

Question 2

Research that analyzes the cognitive development of the same individuals as they develop over the years is called:
 
  cross-sectional research.
  representative samples.
  longitudinal research.
  sequential research.

[Fayaz00962]

Answer to Question 1

cohort differences can make it difficult to differentiate between developmental
change and cohort differences.

Answer to Question 2

longitudinal research.

[joblessjake]

Thank you

[Fayaz00962]

No problem