Data means information or facts obtained and recorded by a political scientists or researcher about some political matter or facts recorded by him. Obviously, data must be accurate, that is, it must correspond to empirical reality or must have some kind of empirical reference located outside the political scientist or researcher. It means that it must be free of his subjective opinion or bias.
As. we said above, before 1945, it was difficult to record data. But the data revolution, which began from about 1945, a very large quantities of data can be stored, analysed or processed and retrieved electronically, such as by computers. Such data storage is called a data bank. Such data banks exist in advanced countries of die world, e.g. U.S.A, Great Britain, France, Germany, etc. It is also possible to establish a world-wide data bank. But a data bank has certain problems: the data stored must be reliable and complete; secondly, it should not be tempered with. In other words, it should not be possible to distort it by means of wrong information or data, called a virus in the language of computer science.
Professor Karl Deutsch has given a list of seven main categories of statistical! data: public opinion data; statistics about popular voting; data about political elites; statistics of voting in legislative assemblies; content analysis data; aggregate administrative data provided by the governments; historical data. To this may be added the data or statistics collected by other social sciences.