These approaches include the use of the online catalog, CUNY Plus, which catalogues books by keyword or by standard subject heading; journal articles; available sources of statistics; the National Criminal Justice Reference Service, and supplementary material. Keyword searching, which requires some skill and is more helpful than standard subject headings for comparative research, picks up words or phrases that appear anywhere among the author, subject, title, and other fields in the computer record that describes each book. In most instances, it is necessary to use an index to locate relevant journal articles. Sources of statistics include special reports; the "International Crime Statistics" that is compiled biennially since 1950 by the International Criminal Police Organization; the U.N. World Crime Surveys which are taken at 5-year intervals since 1976; current national statistics compendiums; and CUNY Plus which includes criminal statistics as one of the catalog's standard subject headings. Since 1972, the National Institute of Justice microfiches material it receives and sends it out to selected libraries. The microfiche collection of the National Criminal Justice Reference Service now numbers over 30,000 documents. Finally, reference books are cited that provide background information on country politics, government, or culture.