Acase study involving a person with 53 different personalities, although valuable in some ways, is unlikely to be

The answer to this question is generalizable
generalizable refers to a case study's capability to be implemented into larger sample of the population. In this particular case study, it is really hard to put the result of 53 personality studies into use because it is almost impossible to find all the indicators of the personality unless we know that specific person' for a pretty long time.

Hope this will !