What is a longitudinal study and what are the advantages of using it in research?

Longitudinal studies (sometimes called prospective studies) follow the same group of individuals over time, typically months or years. Longitudinal studies are employed to investigate a wide range of issues, including areas of physical and mental health and trajectories of behavioural disorders, educational progress and language development. Crucially, longitudinal studies must collect the same information from their participants at every data collection interval. Longitudinal studies frequently use a variety of methods to collect this information, such as, observations, interviews and questionnaires. A major advantages of longitudinal studies is the quantity and quality of the data collected, enabling rich insights into and about the variables of interest, including how they relate to demographic factors, such as, socio-economic status. Longitudinal studies permit exploring continuity and discontinuity of variables, the order in which things happen and the potential causes of these things. Longitudinal studies also benefit from reduced risks of recall bias as the researcher can check participant responses with their prior data collected. Furthermore, longitudinal studies enable identifying findings simply due to participants growing older (referred to as 'age effects') and those better explained by particular historical, economic and/or social contexts (referred to as 'cohort or generational effects').