Professor Fischer uses the sequential research method. In the problem, Professor Fischer observes three different age groups over a period of 10 years periodically to take note of the changes in memory; this is a clear example of the sequential research method. Sequential research method is also known as cross-sequential study that uses and combines the longitudinal design and cross-sectional design study. Its purpose is to correct the problems that were inherent in the cross sectional and longitudinal designs.
Both longitudinal and cross-sectional are observational studies and researchers usually do not interfere with their subjects. Professor Fischer’s action on observing 3 different age groups is called longitudinal study, but he also takes note of the changes, that makes him gathering the data which is most commonly a cross-sectional study. Combination of these two is called sequential study.