About The I Index
The I Index is a ranking of the most influential nonfiction books in English. Each book is scored across three dimensions — critics, readers, and scholars — and its overall I Index is the average of all three.
How the scores are calculated
Critics Index
The Critics Index is based on reviews aggregated from the following publications:
Associated Press · The Atlantic · BookPage · Bookforum · Booklist · Bookreporter · The Boston Globe · Chicago Tribune · The Chicago Review of Books · The Christian Science Monitor · The Economist · The Evening Standard · The Financial Times · The Globe and Mail · The Guardian · Harpers · The Irish Times · Jacobin · Kirkus · Library Journal · London Review of Books · Los Angeles Review of Books · Los Angeles Times · The Minneapolis Star Tribune · The Nation · Nature · The New Republic · New York Review of Books · The New York Journal of Books · The New York Times · The New Yorker · Newsday · NPR · Publishers Weekly · San Francisco Chronicle · The San Francisco Book Review · Science · Shelf Awareness · Slate · The Spectator (UK) · The Telegraph (UK) · Times Literary Supplement · The Times (UK) · USA Today · The Wall Street Journal · The Washington Post
The Critics Index is the average of two sub-scores, each expressed as a percentile from 1 to 99 relative to all books in the index: a volume score based on the number of reviews a book has received, and a rating based on the level of praise or criticism in the review.
Readers Index
The Readers Index is drawn from multiple sources of reader ratings. It is the average of two sub-scores: a volume score based on the number of ratings a book has received relative to the time since its publication, and a value score based on the average rating. Both are expressed as percentiles from 1 to 99.
Scholars Index
The Scholars Index is based on the number of citations a book has accumulated relative to the time since its publication, expressed as a percentile from 1 to 99. Only books with a minimum of 5 citations per year are given a score for the Scholars Index.
The I Index
A book's I Index is the average of its Critics Index, Readers Index, and Scholars Index, where all three scores are available. If a book does not meet the threshold for citations, the Index is based only on the Critics Index and the Readers Index.
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