Final answer:
A case study is an in-depth analysis of a single event, situation, or individual. John is conducting a case study by examining records, reports, diaries, and assessments to draw a clinical conclusion.
Step-by-step explanation:
A case study is an in-depth analysis of a single event, situation, or individual. It involves examining existing sources, conducting interviews, and direct observation to gather information. In John's case, he is spending time going through records, reports, diaries, and assessments to draw a clinical conclusion, which is why his activity is referred to as a case study.