Think tanks vary by ideological perspectives, sources of funding, topical emphasis and prospective consumers. Some think tanks, such as The Heritage Foundation, which promotes conservative principles, and the Center for American Progress, a progressive organization, are more partisan in purpose. Others, including the Tellus Institute, which emphasizes social and environmental topics, are more issue-oriented groups.
Funding sources and the consumers intended also define the workings of think tanks. Some receive direct government assistance, while others rely on private individual or corporate donors. This will invariably affect the degree of academic freedom within each policy institute and to whom or what the institution feels beholden. Funding may also represent who or what the institution wants to influence; in the United States, for example, "Some donors want to influence votes in Congress or shape public opinion, others want to position themselves or the experts they fund for future government jobs, while others want to push specific areas of research or education."
A new trend, resulting from globalization, is collaboration between policy institutes in different countries. For instance, the Carnegie Endowment for International Peace operates offices in Washington, D.C., Beijing, Beirut, Brussels and Moscow.
The Think Tanks and Civil Societies Program (TTCSP) at the University of Pennsylvania, led by Dr. James McGann, annually rates policy institutes worldwide in a number of categories and presents its findings in the "Global Go-To Think Tanks" rating index. However, this method of the study and assessment of policy institutes has been criticized by researchers such as Enrique Mendizabal and Goran Buldioski, Director of the Think Tank Fund, assisted by the Open Society Institute.
Several authors have indicated a number of different methods of describing policy institutes in a way that takes into account regional and national variations. For example:
Independent civil society think tanks established as non-profit organisations—ideologically identifiable or not;
Policy research institutes affiliated with a university;
Governmentally created or state sponsored think tanks;
Corporate created or business affiliated think tanks;
Political party think tanks and legacy or personal think tanks;
Global (or regional) think tanks (with some of the above).
Alternatively, one could use some of the following criteria:
Size and focus: e.g., large and diversified, large and specialized, small and specialized;
Evolution of stage of development: e.g., first (small), second (small to large but more complex projects), and third (larger and policy influence) stages;
Strategy, including: Funding sources (individuals, corporations, foundations, donors/governments, endowments, sales/events). and business model (independent research, contract work, advocacy); The balance between research, consultancy, and advocacy; The source of their arguments: Ideology, values or interests; applied, empirical or synthesis research; or theoretical or academic research (Stephen Yeo); The manner in which the research agenda is developed—by senior members of the think tank or by individual researchers, or by the think tank of their funders; Their influencing approaches and tactics (many researchers but an interesting one comes from Abelson) and the time horizon for their strategies: long term and short term mobilisation; Their various audiences of the think tanks (audiences as consumers and public -this merits another blog; soon) (again, many authors, but Zufeng provides a good framework for China); and Affiliation, which refers to the issue of independence (or autonomy) but also includes think tanks with formal and informal links to political parties, interest groups and other political players.