A question about schwag

As an obscure critic for an alt-weekly, I don't rate too highly with publicists. Nevertheless, occasionally I get goodies along with a game. My favorite was the chocolate-covered Oreos Nintendo sent along with Metroid Prime 2: Echoes, and I did ironically wear a Grand Theft Auto: San Andreas hat from Rockstar. Rockstar is pretty good about sending schwag, actually. They included a t-shirt along with Bully. But how do they know they should send shirts to critics in size XL?