Participant observers study people in their natural environment, gaining
a depth of insight into behaviour that comes not simply from close,
detailed, observation but also from the researcher's own experiences within the
group being studied - a technique that provides first hand insights into
why people behave as they do.
In addition, participant observation does not prejudge issues and events (in the way a questionnaire may, for example) and, for these reasons it is possible to argue that such a method provides data that has a high level of validity.