What Makes A Good Index

A good index retains the author’s terminology, and anticipates the expectations of different readers. In other words, an index does not exist independently of its audience.” Nancy Mulvany in Indexing Books

What Are the Qualities of a Good index?

  • A good quality index is recognized by readers as having “real value” because they can find information quickly and efficiently with a well written index. Readers prefer to buy books with well written, detailed and organized indexes.
  •  A quality index is a mark of a serious book: written to generally accepted indexing standards: it performs flawlessly. Readers find what they are looking for and don’t give the index a second thought. If on the other hand, the index is poorly written, readers become frustrated and will very likely move on the the next book.
  •  A good book index anticipates how readers will search for information. The index provides immediate access to the important terms, concepts and names scattered throughout the book, quickly and efficiently.
  •  A good index has headings and subheadings that are concise, accurate and unambiguous, reflecting the contents and terminology used in the text.
  •  A good index has enough cross-references to connect related terms; appropriate alphabetization and page references format to assist with reading the index; and the index is comprehensive with an appropriate length and level of detail.
  •  A quality book index reveals the interrelationships of topics, concepts and names so that readers need not read the whole index to find what they are looking for.
  •  A good index provides terminology that may not be used in the text, but which the reader will use for searching through the index.
  • Quality book indexes are written with the readers in mind: book indexing is something that only human book indexers can do well. Automatic indexing software  produce a “concordance” or list of words that have limited usefulness.

Benefits of a Good Index

  • Studies show that a quality back of book index increases book sales. Readers, book reviewers, academics and librarians are less likely to buy or even recommend a book without an index. So authors and publishers rely on professional book indexers to write back-of-the-book indexes for them.
  •  A good quality index is a mark of a serious book. When written to generally accepted indexing standards, the index performs flawlessly, and readers find what they are looking for and don’t give the index a second thought. If however, the book lacks an index, or the index is poorly written, readers becomes frustrated and simply go to the next book. The book sale is lost.

Evaluating an Index

Step 1: General

  • Are the indexing terms appropriate for the intended audience?
  •  Is the style of the index appropriate? (e.g. indented versus run-in style)
  • Is the index length appropriate for the level of complexity of the book? As general guide, indexes should be 3-5% of the total number of pages for typical nonfiction books; 5-8% for textbooks; and 15-20% for reference books.
  •  Is the type size and font easy to read?
  •  Is the organization of headings and subheadings easy to read? Are entries concise and clearly written?
  •  Are there any spelling or grammar mistakes in the index?
  • Is the punctuation clear and consistent?

Step 2: Headings

  • Are the headings relevant?
  •  Have the key concepts in the book been identified?
  •  Are headings specific, pertinent and comprehensive?
  •  Are there more than 5 or 7 locators per header? if so, subheadings should be added.
  •  Are references to a single topic scattered among several headings? Can they be consolidated under a single heading?

Step 3: Subheadings

  • Are subheadings useful?
  •  Are subheading entries wordy or concise? Have they been edited to remove unnecessary words/phrases?
  •  Is the number of subheadings about right? Are there too many? Are they over analyzed? Could some subheadings be combined?
  •  Have the prepositions ‘a’, ‘an’, ‘and’, and ‘the’ been removed from the beginning of subheadings?
  •  Do subheading have more than 5 to 7 locators (page references)? If so, they should be broken down into additional subheadings.
  •  Are there any subheadings with the same keyword/phrase? Is so could they be made into a separate header under that keyword, with a cross-reference back to the original header?
  •  Have subheadings been double-posted to make main headings, for the reader’s convenience? Do the double-postings have the identical locators?

Step 4: Locators (Page References)

  • Are the locators accurate? Spot-check several subheadings for accuracy and comprehensiveness of the locators.
  •  Are there more than 5 to 7 undifferentiated locators after a header or subheading? If so, they should be broken down into additional subheadings.
  •  Are there any false locators, or locators missing an en dash (e.g. “172-72”, or “13102”)

Step 5: Cross-References

  • Have cross-references See, and See also been used correctly? (e.g. ‘See’ should point to a term that expresses the same concept; while ‘See also’ should point to related information.
  •  Are any cross-reference circular?
  •  Are more cross-references required to help the reader navigate the index?

Cook Index Usability Studies

Book index usability studies examine effectiveness of indexes for locating and retrieving information quickly; how they add value to a book and increase book sales; and the relationship between quality indexes and Pulitzer Prize awards. The usability studies have found that indented indexes are preferred over run-in style; that there is a learning curve for users only familiar with text searching on the Internet; that some users expect index headings to be like a “table-of-contents; while other users would like more cross-references in indexes.

1. Susan Olason’s Index Usability Study

Olason’s usability study found that “Indexes directly affect publishers’ profits and add value to authors’ reputation by making their knowledge accessible in a user-friendly manner.” Two key factors influencing book selection were: comparing book indexes and the price of the book. The study also found that indented indexes are preferred over run-in style; that users expected headings to be like a “table-of-contents”; and that some readers were frustrated by having to read rather than scan the index.
(Source: “Let’s get usable! Usability Study for Indexes”, by Susan C. Olason, The Indexer, Vol. 22, No. 2, October 2000)

2. BNA Law School Index Usability Study

BNA’s usability study compared the speed and success in finding specific legal information using indexes versus text searches. BNA concluded that an index provided more relevant and complete results (86 percent versus 23 percent success rate for indexes versus text searches.) Secondly, index users frequently discovered other related information in sub-headings, and this was considered a real bonus.
(Source: “Using on-line Indexes”, The Bureau of National Affairs, Inc., 2008)

3. Macmillan Computer Publishing Index Usability Study

The Macmillan usability study made a number of recommendations to improve information retrieval from indexes. (Source: Usability Testing at Macmillan USA” by Christine Nelsen Ryan and Sandra Henselmeier, Key Words, Vol. 8, No. 6 November/December 2000)

4. Barnum Index Usability Study of User Preference and Performance

The Barnum usability study looked at information retrieval using a hyper-linked index versus full-text search in an electronic text. The study found that index readers used the table of contents in addition to the index; and that users liked a lot of synonyms in an index. The study identified issues affecting user performance and attitude, and the study made a number of recommendations for additional research. (Source: “A Usability Study of User Preference and Performance” by Carol Barnum et. al., Technical Communication, Vol. 51, No. 2, May 2004.)

5. Indexes in Pulitzer Prize winning books

The Sassen usability study investigated whether there was a correlation between index quality and a book awarded the Pulitzer Prize for nonfiction between 1962 and 2008. The study found that “the ratio of index to book pages increased during the period 2000-2008, and there is trend towards more indexes in award-winning indexes.” (Source: “Indexes in Books Awarded the Pulitzer prize for General Nonfiction (1962-2008), by Catherine Sassen, Key Words, January-March 2009)

6. Usability study of academic library website indexes

The Kingsley usability study examined the use of back-of-the-book style indexes for websites in terms of end-user use, speed and accuracy of finding information, and end-user perception of the web indexes. The study found that (1) participants were more successful finding information using a website index, and (2) that academic library site indexes were effective navigational tools. Some users however did not think to use the website index even after failing to get results by searching and browsing.(Source: “The usability of academic library website indexes” by Ilana Kingsley. The Indexer, Vol. 26, No. 2, 2008.)

7. Jorgensen and Liddy Usability study

Corinne Jorgensen and Elizabeth D. Liddy’s usability study found that index users became more efficient as they learned the structure of an index. A back-of-the-book index has an intuitive structure that can be readily grasped, and users can become very proficient in accessing information. (Source: “Information access or information anxiety? – an exploratory evaluation of book index features” by Corinne Jorgensen and Elizabeth D. Liddy. The Indexer Vol 30 No. 2 October 1996.


“A nonfiction book without an index has no heft. I pay it no attention.”
Arthur Salm (San Diego Tribune book reviewer/editor)

William Shakespeare: “Ah me, what act that roars so loud and thunders in the index?” Hamlet, Act III, Scene 4.

The London Times, May 8, 1957: “The inclusion of an index is, of course, not enough in itself. It must be a good index.”

Book published in 1465: “The index and figures of this book are indeed alone worth its whole price, because they make it much easier to use… so that everybody who wants to quickly find something contained in this little book, can find it.”