What is a longitudinal study?

Why might they be particularly helpful in clinical research?

Bradshaw (1998) notes that often studies of CBT for example have only charted the participants’ experiences for relatively brief periods of experimental treatment with brief follow-up and there has been little research that has looked at the “application of CBT to the multiple problems of clients with schizophrenia over the long-term course of the disorder”. This means that the conclusions of studies looking at the benefits of different forms of treatments may not go on for long enough to get valid measure of relapse and remission for example.

https://www.researchgate.net/publication/49780069_Longitudinal_imaging_studies_in_schizophrenia_The_relationship_between_brain_morphology_and_outcome_measures