Everything we know about any psychological disorder is a result of past research. This research has taken on many different forms. An individual case study is often used in psychological research; however in studying abnormal behavior the results of only one individual cannot be applied across larger populations so this method is not used as often. Correlational research looks at the relationships between variables. For example, a researcher might look at the amount of time one spends in the sun to see if it correlates with depression, because a certain form of depression has been linked to a lack of time in the sun (known as Seasonal Affective Disorder). To study the effects of a medication or treatment, researchers often rely on experimental research, in which a comparison can be made between a group that received a particular treatment over another that did not. We will also explore how researchers have studied behavior across time, culture, and lifespan development. But what about studying the effects of environment versus genetics? While individual case studies and correlational and experimental research can provide psychologists with a great deal of information on the effects of abnormal behavior, when looking at causal factors regarding genetics or environment, researchers must look at familial history. A good deal of our understanding on the influence of environment and genetics has been derived from three primary types of studies: family studies, twin studies and adoption studies. The most compelling research of all these types of studies are the twin studies—particularly those studies of twins who were separated at birth. 1. Which type of research do you think would be most helpful in understanding abnormal behavior? 2. Why might twin studies give us such compelling evidence regarding the influence of genetics? 3. Can you think of any ways that twin studies could be combined with other types of research to give us more insight into human behavior and particularly into psychological disorders?