Research reports in the sciences and social sciences. Especially for recent social history, the best evidence of broad developments in society is often in the form of social science surveys or research studies. This research may be reported in book form, government reports or most commonly in articles published in scholarly journals. Since these are generally very limited in availability and in what they reveal, however, it is also possible to make use of ideas and images conveyed in the mass media, and even in literature, film, popular fiction, self-help literature, textbooks, etc. Again, the point is to use these sources, written or produced at the time, as evidence of how people were thinking.
Secondary sources are works that interpret or analyze an historical event or phenomenon.
They are generally at least one step removed from the event. Encyclopedias and textbooks are also examples of secondary sources.