Psychologists who study psychological disorders, along with practitioners who treat disorders, often utilize a particular theoretical perspective. Each perspective attempts to explain the origin of a disorder and/or determine the best method for treatment. These explanations and treatments build on the history, theories, and perspectives introduced in the units 2 and 3 as well as on cognitive psychology in particular. Through observing behavior and engaging in discussion that illuminates a client’s thought process, psychologists gather information and draw conclusions. For some psychologists, a single perspective cannot fully explain a disorder. This leads them to more integrated perspectives to understand and treat psychological disorders.