Naturalistic observation involves systematically observing and recording behaviors as they naturally occur. It allows researchers to study human behaviors that cannot be experimentally manipulated. This method can be used to openly observe patterns of behavior wherever they occur. Case studies provide intensive examinations of individuals or small groups and can reveal information about normal behaviors from rare or unusual cases. Surveys use questionnaires or interviews to gather information from large groups about behaviors, attitudes, and opinions using representative samples and random selection. Correlational studies examine relationships between variables without manipulation and use correlation coefficients ranging from -1 to +1 to indicate the strength and direction of those relationships.