A psychologist who is studying the mathematical abilities of ...

[lilldybug07]

A psychologist who is studying the mathematical abilities of adults finds significant differences between the scores of adults born 50 years ago, when rote learning was stressed,
 
  and those born 25 years ago, when more progressive approaches to education were popular. This is an example of a(n)
 
  failure of longitudinal research.
  advantage of cross-sectional research.
  cohort difference.
  intellectual decline in middle adulthood.

Question 2

A problem with longitudinal research on intelligence is that
 
  it is usually distorted by cohort effects, especially in older participants.
  few people participate in such research voluntarily.
  people of lesser intelligence tend to volunteer for retesting.
  practice on the test items may produce learning.

[cat123]

Answer to Question 1

cohort difference.

Answer to Question 2

practice on the test items may produce learning.

[lilldybug07]

Great answer, keep it coming

[momolu]

Excellent