Women often avoid clothing with horizontal stripes, believing the pattern makes them look wider than they actually are. Now new research has proven that to be true.

Back in 2008, 2D line drawings of people in horizontal stripes were shown to volunteers who said they made the wearers look thinner. But Val Watham thought things would be different in the 3D realm, so she conducted her own set of experiments using live models.

Sure enough, those wearing horizontal stripes were judged to be wider, while those wearing vertical stripes were thought to be taller. And that old adage about black clothes being slimming? Also held true.

Waltham’s experiment beat out over 1,000 other entrants to win the BBC’s Amateur Scientist of the Year award, with the judges saying her work was “a lovely idea which was well executed, had clear results and leads on to further research. You can’t ask more from a science experiment.”