Longitudinal data is a collection of information about a group of people at different points in time. This information is helpful in assessing change over a significant time period. For instance, a psychology researcher wanted to measure how a group of individuals’ behaviors had changed since childhood. The subjects were then interviewed and assessed every year. The information which were collected for 15 years were then analyzed.
One famous example is Walter Mischel’s Marshmallow Test. He measured the ability of pre-school children to delay gratification and tracked them until their adulthood. The longitudinal data concluded that those who were able to be more patient fared better in life. Hence, good things come to those who wait.