How We Rank Books

The Ideas Index ranks nonfiction books published since 2020 by combining three independent signals: how readers rate them, how critics assess them, and how often scholars cite them. Each signal is processed separately, adjusted for known biases, and then averaged into a single score on a 1–99 scale. Here is exactly how it works.

1. Which Books Are Included

To appear in the index, a book must satisfy three conditions. It must have been reviewed by at least two critics from the publications we track. It must have a substantial number of reader ratings collected from major book rating platforms. And it must have been originally published in 2020 or later. Books that meet these thresholds form the eligible pool — currently around 4,000 titles — against which all percentile scores are calculated.

Books are organized into 18 subject categories: Biography, Business, Criticism, Culture, Essays, Film & TV, Health, History, Memoir, Nature, Poetry, Politics, Religion, Science, Social Sciences, Sports, Technology, and True Crime. Category assignments come from our critic-review data where available and fall back to reader-platform genre tags otherwise.

2. The Three Signals

Reader ratings

We aggregate reader ratings from multiple sources. The raw average rating a book receives is a useful signal, but it is distorted by a well-known genre effect: readers in some categories tend to rate generously while readers in others tend to rate more stringently. A 4.1 average in Biography is not the same achievement as a 4.1 in Memoir.

To correct for this, we apply Bayesian shrinkage toward each book's category mean. The adjusted rating is a weighted average of the book's own observed rating and the mean rating for its category, with the weights determined by how many ratings the book has received. Books with thousands of ratings are barely moved — the data speaks for itself. Books with only a handful of ratings are pulled substantially toward the category average, reflecting our genuine uncertainty about where they will settle once more readers weigh in. The adjusted ratings are then converted to a percentile score from 1 to 99 relative to all eligible books.

Critic assessments

We collect review data from the following publications and outlets: Associated Press, BookPage, Bookforum, Booklist, Bookreporter, Chicago Tribune, Financial Times, Harper's, Jacobin, Kirkus, Library Journal, London Review of Books, Los Angeles Review of Books, Los Angeles Times, NPR, Nature, New York Review of Books, Publishers Weekly, San Francisco Chronicle, Science, Shelf Awareness, Slate, The Atlantic, The Boston Globe, The Chicago Review of Books, The Christian Science Monitor, The Economist, The Evening Standard, The Guardian, The Irish Times, The Minneapolis Star Tribune, The Nation, The New Republic, The New York Journal of Books, The New York Times, The New Yorker, The Spectator (UK), The Telegraph (UK), The Times (UK), The Wall Street Journal, The Washington Post, Times Literary Supplement, and USA Today.

Because some outlets tend to be consistently more generous and others more demanding, a statistical process is applied to estimate each outlet's rating tendency and adjust for it across all reviews. This ensures that a rave from a characteristically tough publication carries more weight than a rave from one that rarely publishes a critical word.

We also adjust for the number of reviews a book has received. A book with only two reviews provides less reliable signal than one with a dozen, so books with few reviews are partially pulled toward their category's average — reflecting genuine uncertainty rather than treating a thin sample as definitive. The adjusted critic ratings are then converted to a percentile score from 1 to 99 relative to all eligible books.

Scholar citations

For books that have entered academic conversation, we collect citation counts. Because newer books have had less time to accumulate citations, we annualize the citation count — dividing by the number of years since publication — to put books published in 2020 on comparable footing with books published in 2024. Books receiving fewer than five citations per year are treated as having no meaningful scholarly footprint and receive no Scholar score; they are not penalized, but citations do not factor into their final index. Books above that threshold are ranked against the full eligible pool, with non-qualifying books treated as ranked below all qualifying ones. The result is a Scholar score from 1 to 99 that reflects a book's uptake in academic and intellectual discourse relative to its peers.

3. The Final Score

The Ideas Index score is the simple average of whichever component scores are available for a book. For a book with meaningful citation data, the score averages the Reader Rating score, the Critic Rating score, and the Scholar score equally. For a book without significant citations, the score averages only the Reader Rating and Critic Rating scores. No component is double-counted, and no component is treated as more important than the others.

All scores run from 1 to 99 and represent a book's percentile position within the eligible pool. A score of 75 means the book outperforms 75 percent of the books in the index on that measure. Scores are divided into four tiers:

Top of the Pile — scores 75–99

Near the Top — scores 50–74

Maybe Someday — scores 25–49

Bottom of the Pile — scores 1–24

4. Updates and Corrections

The index is updated periodically as new books become eligible and as existing books accumulate more ratings, reviews, and citations. Because all scores are percentile-based, updates will shift every book's score slightly as the pool grows. If you notice an error in a book's data — a wrong citation count, a misattributed review — please use the contact link below to let us know.

Privacy Policy

At I Index, we prioritize your privacy and are committed to protecting your personal information. This Privacy Policy outlines how we collect, use, and safeguard your data when you interact with our website.

1. Information We Collect

2. How We Use Your Information

3. Sharing Your Information

We do not sell, trade, or otherwise transfer your personally identifiable information to outside parties except to trusted third-party service providers who assist us in operating our website, conducting our business, or serving our users — provided those parties agree to keep this information confidential.

4. Your Rights

You have the right to access, correct, or delete the personal information we hold about you. To exercise these rights, please contact us through the site.

5. Changes to This Policy

We may update this Privacy Policy from time to time. We will notify you of any significant changes by posting the new policy on this page with an updated date.