The "Atlas Shrugged" index

The Economist reports that sales of Ayn Rand's master tome spike whenever capitalism takes it on the chin:

Reviled in some circles and mocked in others, Rand's 1957 novel of embattled capitalism is a favourite of libertarians and college students. Lately, though, its appeal has been growing. According to data from TitleZ, a firm that tracks bestseller rankings on Amazon, an online retailer, the book's 30-day average Amazon rank was 127 on February 21st, well above its average over the past two years of 542. On January 13th the book's ranking was 33, briefly besting President Barack Obama’s popular tome, "The Audacity of Hope".