Stanislas Dehaene and colleagues surveyed Mundurucu participants (in the Amazon) and Western participants (in the USA) on where they felts numbers lie on a scale from from 10-100. When expressing changes in probabilities, it makes us nervous that people can play games. They can choose between small numbers (here catch rates) and large numbers (drop rates) to play up or play down a point. This post discusses how this can happen whether one uses relative risk calculations or simply provides before and after numbers. This is one reason we are fans of providing absolute changes in probability. Going from Coach A to Coach B, catches decreased 8 percentage points, which is to say drops increased by 8 percentage points. With this formulation, no matter how the thing is expressed, the only thing the forgetful can get wrong is the sign.