Which of the following statements is true of a longitudinal study?
1) In this study, people of different ages are assessed at one point in time, and differences are noted.
2) In this study, people of the same age are assessed at different points in time, and changes are observed.
3) In this study, people of different ages are assessed at different points in time, and changes are observed.
4) In this study, people of the same age are assessed at one point in time, and differences are noted.