Political science is a social science which deals with systems of governance, and the analysis of political activities, political thoughts, and political behavior.Political scientists may serve as advisers to specific politicians, or even run for office as politicians themselves. Political scientists can be found working in governments, in political parties or as civil servants. They may be involved with non-governmental organizations (NGOs) or political movements. In a variety of capacities, people educated and trained in political science can add value and expertise to corporations. Private enterprises such as think tanks, research institutes, polling and public relations firms often employ political scientists. Political science is a social science which deals with systems of governance, and the analysis of political activities, political thoughts, and political behavior. Political science—occasionally called politicology—comprises numerous subfields, including comparative politics, political economy, international relations, political theory, public administration, public policy, and political methodology. Furthermore, political science is related to, and draws upon, the fields of economics, law, sociology, history, philosophy, geography, psychology/psychiatry, anthropology and neurosciences. Comparative politics is the science of comparison and teaching of different types of constitutions, political actors, legislature and associated fields, all of them from an intrastate perspective. International relations deals with the interaction between nation-states as well as intergovernmental and transnational organizations. Political theory is more concerned with contributions of various classical and contemporary thinkers and philosophers. Political science is methodologically diverse and appropriates many methods originating in psychology, social research and cognitive neuroscience. Approaches include positivism, interpretivism, rational choice theory, behaviouralism, structuralism, post-structuralism, realism, institutionalism, and pluralism. Political science, as one of the social sciences, uses methods and techniques that relate to the kinds of inquiries sought: primary sources such as historical documents and official records, secondary sources such as scholarly journal articles, survey research, statistical analysis, case studies, experimental research, and model building. Political scientists study matters concerning the allocation and transfer of power in decision making, the roles and systems of governance including governments and international organizations, political behaviour and public policies. They measure the success of governance and specific policies by examining many factors, including stability, justice, material wealth, peace and public health. Some political scientists seek to advance positive (attempt to describe how things are, as opposed to how they should be) theses by analysing politics. Others advance normative theses, by making specific policy recommendations. Political scientists provide the frameworks from which journalists, special interest groups, politicians, and the electorate analyse issues. According to Chaturvedy, In the United States, political scientists known as 'Americanists' look at a variety of data including constitutional development, elections, public opinion, and public policy such as Social Security reform, foreign policy, US Congressional committees, and the US Supreme Court — to name only a few issues. Because political science is essentially a study of human behaviour, in all aspects of politics, observations in controlled environments are often challenging to reproduce or duplicate, though experimental methods are increasingly common (see experimental political science). Citing this difficulty, former American Political Science Association President Lawrence Lowell once said 'We are limited by the impossibility of experiment. Politics is an observational, not an experimental science.' Because of this, political scientists have historically observed political elites, institutions, and individual or group behaviour in order to identify patterns, draw generalizations, and build theories of politics. Like all social sciences, political science faces the difficulty of observing human actors that can only be partially observed and who have the capacity for making conscious choices unlike other subjects such as non-human organisms in biology or inanimate objects as in physics. Despite the complexities, contemporary political science has progressed by adopting a variety of methods and theoretical approaches to understanding politics and methodological pluralism is a defining feature of contemporary political science.