Theme indexes typically provide annotated bibliographies of fictional works along with an index that identifies which themes are present in which works. For example, a theme index of U.S. fiction related to social themes published in the first half of the 20th century would include an annotated bibliography of U.S. works published during that period along with an index of themes such as abortion, abuse, dating, race relations, religious issues, and more.
Short stories and novels can be important primary resources for research in history and literature, and the ability to identify works about specific issues can be an extremely useful is supporting efficient research.