Simply Psychology lists several different designs for psychological experiments, four of which are case studies, observational study, interview and content analysis. Wikipedia differentiates methods and designs based on the sources of information, how the information is collected and the tools used to collect information.
According to Simply Psychology, case studies involve in-depth studies of an individual, group of people, community or event. Observational studies are defined, as involving a researcher observing a group of people either by posing as a member of that group or informing the group that they are being observed as part of a study. Interviews are when a researcher asks a subject questions either in a conversational or more formal sense. Content analysis uses indirect observation by researchers to analyze the presence and meanings of words and images to make inferences about messages in various media.