Theoretically grounded research illuminating mechanisms of legal effect has at least three important benefits for public health law research and practice: Defining the phenomena to be observed, supporting causal inference, and guiding reform and implementation. The choice of what theory or theories to draw upon is a practical one based on research questions and designs, types of law or regulatory approach under study, and state of current knowledge about the matter being investigated. PHLR researchers can draw upon a variety of theories developed by socio-legal scholars to explain how laws are put into practice and how they influence environments and behaviors. Similarly, it is possible to integrate laws within general social and behavioral theories. And it is in fact possible to do both at the same time. These methods make it possible to substantially improve the validity, utility and credibility of health research on effects of laws and legal practices.

This guide first elaborates on why it is so important to investigate how, as well as whether, law is having an effect on health, using safety belt laws as one example. It then uses a second example in greater detail — the health effects of criminal laws regulating HIV exposure through sex — to illustrate how diverse theories of legal effect can be productively used.