Think tanks are organizations, institutions, or groups that conduct research, and they also produce and disseminate reports and policy recommendations. The focus of these organizations ranges from as narrow as a single issue to very broad. Politically they range from left to right, while some maintain a non-partisan position. Think tank reports are often a good source for current statistics. Think tanks belong to a category called "grey literature." Grey literature exists outside of and is uncontrolled by the usual academic and commercial publishers. Along with policy papers and reports, grey literature also includes conference proceedings, working papers, briefs, hearings, etc.