This indicator is based on the idea that US stocks perform better in years when the model gracing the cover of Sports Illustrated's annual swimwear edition is American.
Created in 2000 by Bespoke Investment Group, the index has a decent-enough track record, being broadly correct between 1978 and 2012. However, that's not to say that it hasn't been glaringly wrong on occasion...
Just to confuse matters further, there are four cover models this year: Americans Kim Kardashian, Ciara, and Yumi Nu, and Canadian-South African Maye Musk.