A theory describes what factors or relationships influence behavior and/or environment and provides direction on how to impact them. Theories used in HIV prevention are drawn from several disciplines, including psychology, sociology and anthropology. A theory becomes formalized when it is carefully tested with the results repeatable in a number of different settings, and generalizable to various communities.

Both formal and informal (or implicit) theories first begin with an individual’s observation about a person or phenomenon. Informal theories—those conceived by service providers— are not usually “tested,” yet these intuitive beliefs about why people do what they do are very useful and often similar to concepts found in formal theories conceived by academics.

Theories can help providers frame interventions and design evaluation. When designing or choosing an intervention, theory can show what factors should be targeted and where to focus interventions. Theories can help define the expected outcome of an intervention for evaluation purposes. Also, basing programs on a tested theory gives it scientific support, especially if the program hasn’t been evaluated.

HIV prevention providers are frequently required to use theory in the development of prevention interventions. It’s common, though, for providers to pick a theory based on their intervention. Because many providers are not trained or supported in using theory, they can miss the opportunity to use it as a process for thinking critically about a community in the development of programs.