Case studies allow data to be gathered that is in depth and detailed and they usually study an individual or group of people who are connected in some way. Whoever is being studied becomes the focus of the case study.
Case studies tend to be reliable because they use many different research methods meaning that triangulation can be used and data can be compared. They also tend to be valid because data is gathered within a natural environment.
However, they are not usually replicable because they concern unique individuals at specific moments in time. This also means that they are not representative to the wider population so results cannot be generalised.
Within child psychology they are useful for psychologists who deal with unique children who have unique difficulties. With children like Genie they can give the depth of data necessary for an effective intervention. They are also often longitudinal so can show development over time.
There are issues of consent when it comes from the parent and not the child because the child’s consent must be considered. It can also be hard to maintain confidentiality over time, even when fake names such as ‘Genie’ are used because details from the case studies can be searched on the basis of interest in what has happened since.