Case Studies:
Studying or recording one subject, and/or the subject's life and developments over long periods of time (sometimes over the course of their whole lives)
Surveys:
A study tool to collect data amongst several individuals in a population. May be used to find out factual information, or simply one's opinion on a certain topic.
Naturalistic Observation:
Observing subjects in their natural environments! (Like observing a child's behaviors at home, where they feel most comfortable. When observing in places where they may not be comfortable, behavior of the subject is due to change.)
