Strength = rich detailed insight
Increasing validity of data collected (Instead of an experiment that assess just one aspect of behaviour, for example)
Strength = enables study of unusual behaviour
Some behaviours/conditions are very rare (eg HM) and don’t be studied using other methods
Limitation = prone to researcher bias
Conclusions are based on the subjective interpretation of the researcher and personal accounts
May reduced the validity of the study
Limitation = small samples
Sample may be on individual/event with unique characteristics
Makes it difficult to make generalisations => low external validity