Case Study:  In a case study the survey  is based on one or more samples. Study on the  respondent(s) can be  investigated in  depth, which  is not possible with  large number of  sample.  In this  type of  research,  the researcher can find out  large variety of  information about each case specially when very  little is known  about the subject. 1t is preferred when information in  greater details  is needed. It probes deep into the factors of interest. The approach  is used when  a  survey with a  large sample or an experiment is  inappropriate, inadequate, or both. 

Case studies can also be made of  individuals from certain recognized groups-  drug addicts, alcoholics, delinquents, professionals, and subjects belonging to particular ethnic groups, on institutes such as schools, factories, hospitals. It may use past history, description of present events;  it could use combination of various methods such as verbal description, observation, measurements, records, and artifacts. The method can also be used  to  compare a known  group with  an unknown group.