Professor Sandis Is Interested in the Development of Cognitive Abilities

Professor Sandis is interested in the development of cognitive abilities. So he designs a research study using a cross-sectional design. When interpreting the study, he needs to remember that the results may be biased because

A) this design does not consider maturation
B) the different cohorts grew up in different historical periods
C) this design is only appropriate for stage theories
D) changes over time are not consistent
E) the single cohort may have shrunk over time because people dropped out of the study