Game demos are, in theory, a good way for a consumer to try out a product before they buy it, giving players a chance to see if a game meshes well with them. If designer Jesse Schell is right, though, the availability of game demos is actually cutting sales in half.

During a keynote address at the Gamelab conference in Barcelona, Schell presented sales data gathered from EEDAR, a leading video game research and analytics company, stating that an Xbox 360 game whose marketing promotion with a release trailer instead of a demo will sell an average of 525,000 copies in a six month period.

Compare that to an average 360 game that promotes with both a release trailer and a demo, which nets about 250,000 copies in the same time period. A 360 title sells less than 100,000 if its marketing includes neither.

Of course, this study only accounts for Xbox games – other game trial types, like Sony’s full game trials for Playstation Plus members – could add further insight into players’ purchasing habits after playing demos. Read the full story below.