Case study is an in-depth study of a single case or a few people rather than a population or sample. Researchers focus on a single case, so that they can make detailed observations over a long period of time, something that cannot be done with large samples without costing a lot of money. Case studies are also useful in the early stages of research when the goal is to explore ideas, test and perfect measurement instruments, and to prepare for a larger study. Another advantage of case study is to obtain knowledge on rare cases such as brain damage. An example is the study of Phineas Gage by Dr John Harlow.
Generally case studies are conduct on one person and also only one experimenter tends to collect data, which can leads to bias in data collection and may influence the results more, than in a different designs. It is difficult to identify the definite cause from a case study. Another main criticisms of case study is that data collected cannot be generalised to the wider population. And also because case studies are longitudinal people are likely to leave the study incomplete which can be frustrating to the researcher.
An observation is the planned watching, recording and analysis of observed behaviour as it occurs in a natural setting. Observation research method is a non-experiment design because there is no independent variable for the investigator to make a cause effect conclusion drawn from the observation however sound evidence is important.
The main advantage of observation is that it provides direct access to social phenomena under consideration. Researcher observe and record people behaviour in certain situation rather that asking people what they would do in certain situation. Another strength of observation method is the use of more than one technique of data collection through a triangular process is seen as highly desirable as a primary research strategy and also observation can effectively compliment other research method.
Another advantage of observation is that certain phenomena can meaningfully accessed and properly understood only through observation for example crowd behaviour, social behaviours of animals, and mother-child interaction at home.
However there are limitations to observation such as observer bias, the observer initial neutral disposition may be affected by the process and distorted. And therefore the result would be a personal description of the event by the observer and therefore these description would be subjective and cannot generalised to other situations. Another limitation is that the researcher has little control over the situation he is observing. Survey is a method used for collecting data as reported by a large group of people about their attitudes, beliefs and the likes. People complete the survey or provide the information themselves. This type of data collection is known as self-report.
Surveys are useful to describe the characteristics of a large population, no other research method can provide that general capability. Survey are inexpensive and easily administered from remote location because of the many different means of conducting the survey such as; email, mail and phone.