Most amateurs in the indexing business (students and often times authors) have the mistaken idea that an index is just a more detailed outline of the text. Here’s an excerpt of what the index for a book on health breakthroughs would look like if you stuck to just the outline idea, based on chapter-level topics:
Blood pressure, 21–28 [followed by 16 subheadings]
Brain health and memory, 39–54 [followed by 22 subheadings]
Cancer, 55–72 [followed by 40 subheadings]
Cholesterol levels, 27–38 [followed by 9 subheadings]
Consumer health alerts, 73–102 [followed by 34 subheadings]
Diet and nutrition, 287–305 [followed by 55 subheadings]
Emotional health, 139–54 [followed by 50 subheadings]
Family relationships and health, 155–70 [followed by 13 subheadings]
Heart health, 171–96 [followed by 30 subheadings]
Infectious diseases, 197–208 [followed by 31 subheadings]
Longevity and optimum aging, 209–30 [followed by 32 subheadings]
Men’s health, 247–60 [followed by 22 subheadings]
Natural remedies, 261–86 [followed by 19 subheadings]
Pain remedies (nondrug/natural), 311–40 [followed by 24 subheadings]
Respiratory conditions, 1–20 [followed by 15 subheadings]
Stroke risk, 183–96 [followed by 16 subheadings]
Women’s health, 341–57 [followed by 16 subheadings]
So, you’d be OK if you happened to know these main topics and looked for other topics underneath these. But what if you want to know about breast cancer or asthma breakthroughs, or if you wanted to know what the latest recommendations are about statins? And where’s exercise or weight management (they are main topics on their own in the final index, but are not reflected in the subheadings under these chapter topics as such—information about them is scattered through the text).
It’s important to be aware that an index is a searching and browsing tool meant to provide location information about more detailed as well as more general topics at the main heading level. The main headings are what people will scan for first, then if they see subheadings under the topic of their choice, they will look at those.
So, the main headings are your primary access points for your readers. If you just give priority to that, you’ll be headed in the right direction. Subheadings are just for when you have too many page numbers after a main heading (more than about five or six) that will make the index user flip back and forth from index to text too many times. Then it’s a courtesy to provide more information.
The idea is not just to outline your book for the index user, but to get that person as quickly as possible to the page in the book where the actual information on a topic resides. And it’s rude to make the user spend extra time studying the index to find what they want.
The main heading is the core of the index and deserves priority and respect. Please? Thanks!