During participant observation, which is used in social science studies, the researchers actively become part of the group being investigated. This first-hand, embedded method of collecting information often leads to copious, rich data. However, researchers have opportunities to interfere with the process, and this has the potential to skew results.
When functioning fully inside a setting, participant observers have access to much more material than researchers who are making observations from outside a situation. Individuals within the study often share their lives more freely with someone inside their circle. In addition, the presence of an outside observer sometimes leads to an "observer effect." Participants do not always act naturally when they know they are being watched.
Participant observation also has disadvantages. Data is collected and interpreted through the lenses of the observer. If the researcher has biases and expectations, they potentially affect this process. Researchers are able to overcome the effects of these preconceptions by being aware they exist and looking out for them.
"Reactivity" is another potential issue for participant observers. They relate to the individuals in the study, feel sympathetic and become overly involved. The data is no longer studied with critical and scientific eyes. The observer has the ability to affect the outcome by influencing others. By becoming too personally involved, the observer alters the original circumstances.