The studies for this literature review were selected using a snowball methodology, buttressed by the input of scholarly subject matter experts from universities across the U.S. and abroad. All studies must be peer-reviewed, published in a scholarly journal, and directly relevant to the policy question at hand. To select our studies, we performed multiple keyword searches using scholarly databases, reviewed articles and reports produced by subject experts and professional societies and organizations, and reached out to leading academic experts to ensure we identified all relevant scholarship that met our criteria. For these analyses, we assessed all relevant studies published since 1985, as constituting roughly the most recent generation of scholarship. Studies could include primary, experimental, longitudinal, qualitative and quantitative research in a variety of social science disciplines, as well as meta-analyses and case studies.
Our objective was to aggregate scholarship that adds in some way to the world’s knowledge about the policy issue in question. Adding to knowledge does not necessarily mean drawing new conclusions but can include strengthening existing knowledge by corroborating what prior studies have shown. Our purpose was not to pick and choose research that endorses a particular policy view, nor to evaluate the quality of individual studies, beyond relying on the filter of peer review, but to include the broadest range of relevant scholarship so that users may both obtain an overview of the state of scholarly knowledge on topics that are matters of public debate, and further examine that research if desired. We recognize that the peer-review process is imperfect but we operate on the principle that it represents the best method we have for holding research accountable to both good faith and sound methodologies.