Newspapers love lists of books, usually in the form of end-year-round-ups of best-selling and notable new books. However, for 2016 Author Robert McCrum has compiled a list of the 100 best non-fiction books. These are “key texts in English that have shaped our literary culture and made us who we are”, in the Anglo-American English language tradition, the list covers “essential works of philosophy, drama, history, science and popular culture”.

Indexers love lists too, usually of words to put into indexes. So I thought I’d run a parallel list and take a look, where possible, inside the books at the indexes.

The first summary was published today, 1st February 2016 and he chose The Sixth Extinction: An Unnatural History by Elizabeth Kolbert. Amazon usefully allows us to ‘look inside’ this volume. It does have an index, so what can I say about it?

• It’s a book of over 300 pages, so it is a little disappointing to find an index of about 11 pages. A rule of thumb is about 5% of the pages should be index. So maybe it’s a bit skimpy, I can’t tell without reading the book.
• The index is in set-out layout, with indented sub-headings one under another. This is generally a good thing as it is easier on the reader’s eye to see what is in those subheadings.
• Headings include names of people, organisations, animals, plants and subjects, which is a good range of coverage.
• Where species are named, they have been given separate sub-headings under the main heading. In some cases this gives lots of sub-entries with information all on the same page, which looks a little odd and strings out entries which could have been more compact. Would a reader looking up ‘worms’ want to differentiate between ‘burrowing’ and ‘earthworms’ before heading into the text? Maybe, maybe not. The rule of thumb is more than five locators could be split down into subheadings, but in this case they have been consistent.
• Some headings have gathered longer strings of locators, for example ‘dinosaurs’ has 12 locators. Without subheadings we don’t know what she says about those dinosaurs.
• Headings often have locators and sub-headings. This isn’t wrong as my indexing software tells me it is when I start editing a draft of an index, but if a heading justifies having any sub-headings, it can be more useful for the reader to have all the locators entered into sub-headings, especially if there are more than five locators at the main heading. The locators at the main heading are sometimes the most important parts, sometimes they are the most minor ones that don’t fit with the sub-headings. The reader doesn’t know which they are and it can be frustrating. If space and time are not an issue it can be good to clear the locators away from the main heading into sub-headings or reduce them to the main entries only and highlight them if possible.

Looking at indexes by other people always makes me think about how I would approach a similar text. Writing an index is an art as well as a skill, and we are often constrained by time, money, space and the requirements of the press or the author. Every indexer will create a slightly different index, for any given text.