It is often more desirable to have a longitudinal design which asks the same question at different points in time.
The three kinds of longitudinal design are: trend study which asks same questions to different samples of the target group at different point in time; cohort study which traces changes in cohorts or people belonging to similar organization or lives in similar location experiencing similar life situations eventually; and panel study which asks similar questions to similar group of people over and over again. Trend studies observe how concepts change ultimately. Cohort studies note the historical periods change as time progresses and panel studies examines how people change through time.
Example of Cross-sectional Question:
Asking criminals or people from different demographic sample in December 2007 the following questions:
Q Do you think the justice system is fair?
Longitudinal Design:
Q Do you think the justice system is fair five years ago?
Example of Trend Design :
Asking “Do you think the justice system is fair?” to a group of criminals/people in December 2002 then five years later ask a different group of criminals or people the same question, “Do you think the justice system is fair five years ago?”
Example of Cohort Design:
Asking “Do you think the justice system is fair?” to a group of criminals/ people in December 2002 then five years later ask THE SAME group of criminals or people the same question, “Do you think the justice system is fair five years ago?”
Example of Panel Design:
Asking “Do you think the justice system is fair?” to a group of criminals/ people in December 2002 then Year after Year ask THE SAME group of criminals/people the same question, “Do you think the justice system is fair?” Then ask the reason for their changes in opinion.
