An index, in its traditional form, is an alphabetized list of names, events, ideas, etc. placed at the end of a nonfiction book. In the digital age, an index can also appear on a website or in an ebook. The primary function of an index is to facilitate information retrieval. A good index will gather related information across multiple access points: main headings, subheadings, double posts, and cross-references. Such an organizational scheme greatly enhances the accessibility of information for the reader.
An index is not a concordance. A concordance is simply a list of each occurrence of the keywords in a given text. The structure of an index is much more complex, reflecting an analytical breakdown of the text, which is more useful to the reader.
Does a book need an index?
Yes! The index is an essential reference tool. Researchers and casual readers will often decide whether or not they will read or purchase a book based on the index. The table of contents (a type of index, really) can give a certain idea of what's in the book, but a reader might want to know if a specific person, event, etc. is discussed, and a thorough index can provide that information. A professionally-written index significantly enhances a book's usability.
Can authors index their own books?
While authors can certainly index their own books, hiring a professional indexer is recommended. Even though authors are the experts on their books, they are often 'too close' to the material to be able to think from the perspective of a reader. An indexer bridges the gap between author and reader, accurately relating the concepts of a text and maximizing readers' ability to retrieve those concepts. The index is also prepared in the final steps of publication, and an author can understandably be so exhausted with the whole process that hiring an indexer is a welcome option. Furthermore, authors are likely unfamiliar with the standards and methodology behind indexing, making a professional indexer's expertise indispensable.
Can a computer program generate an index?
No, a computer cannot create an index, though a program could generate a simple concordance or keyword list. As stated above, an index is a complex analysis of a text, and a computer cannot identify related ideas the way the human mind can. That being said, computer software can greatly aid the process of creating an index. There are a few indexing programs available, and I use Cindex to write indexes. The software handles such tasks as formatting, style, and sorting, allowing the indexer to focus on the analytical tasks.
The cost of an index depends on several factors, such as the type of book (i.e. trade book, scholarly, textbook, etc.), text density, and deadline. Rates are approximately $3-6 per page. For a more exact quote, please send me a sample chapter or two from the middle of the book, as well as deadline information and the approximate number of indexable pages.