R2 is most often seen as a number between 0 and 1, used to describe how well a regression line fits a set of data.

FORBES: Why Are There Not More Women Entrepreneurs?

All these have a survivorship bias: investments mentioned at dinner parties, stocks charted in Value Line, entrepreneurs featured in FORBES, stock market histories (does your data set include the --100% compound annual return on Russia over the past century?), available hedge fund performance numbers and every mutual fund ad.

FORBES: Magazine Article