Developmental Psychologists use the longitudinal study as one of two types of studies used to investigate age-related changes. It is a type of developmental study in which the same group of participants is followed and measured at different ages. It may take years to complete. The drawbacks, however, are that it is time-consuming and expensive. Due to the time-spanning nature, participants may die or drop out of the study. This could leave the researcher with a biased study.