Useful for identifying historical research on a topic. Policy Commons platform for objective, fact-based research from the world's leading policy experts, nonpartisan think tanks, and intergovernmental and nongovernmental organizations. The database allows advanced search on millions of pages of books, articles. Definition: A literature review examines scientific sources relevant to a person's research thesis problem and/or a particular question or theory. It also provides critical analysis that summarizes and synthesizes the source materials while demonstrating how an individual's research relates or fits into a broader framework. The Comparative Policy Data Set, CPDS, is a collection of country-level policy and institutional data provided by Professor Klaus Armingeon and colleagues at the University of Bern. It consists of annual data on democratic countries for the period or since their transition to democracy.