Unfortunately, case studies tend to be highly subjective as they collect detailed qualitative data and it is difficult to generalize results to a large population. This therefore makes them subjective as they are harder to analyse as you need to look for general themes and interpretation within the information gathered despite them providing rich, in-depth data which give more detailed information than obtained through methods such as experiments.
Case studies may also be subjective since the researcher studies the same participant over a long period of time therefore their results cannot generalise others. It can also result in an ethical issue which is dependent on individuality and an investigator may get to know the individual well so may lose objectivity making it harder to analyse results from the theoretical as they may interpret their findings in a biased way so they may tend to find what they wish to find or believe to be true
The reliability of case studies is low because it is very difficult to exactly replicate the case study because the results collected apply to the one participant and not to an entire sample of people. Although the method is able to be repeated there is no way of checking the effectiveness and whether the results obtained are correct causing the reliability to be extremely low. However one positive is the use of triangulation to increase internal reliability as the more the methods contrast with each other, the greater the researcher’s confidence is further increasing the trustworthiness of the data further ensuring the quality and validity of the research.
Perhaps the biggest limitation of the case study is the population validity which is particularly low as it is done on one participant who cannot account for all others seeking help as the diagnostic is individually created for each person therefore cannot be generalised.
Unlike most scientific experiments internal validity is likely to be poor