Answer:
Typical case sampling
Step-by-step explanation:
Purposive sampling is a type of sampling in which the sample is chosen according to specific criteria.
In typical case sampling the researcher wants to know the trends of a certain criteria. Generally what is mostly to be expected from a group's characteristic is found out using typical case sampling.
Here, what is most commonly found in clients in terms of symptoms, length of treatment, etc is asked. Hence, this is an example of typical case sampling