Janice is a journalism student at OSU who works for the Lantern (the school newspaper). She is interested in seeing what students think about a new rule change regarding fraternity housing. In order to obtain a representative sample of OSU students for public opinion poll, she chooses students whose characteristics correspond to those of the overall student body. For example, she knows that 60% of OSU students are women, so Janice makes sure that 60 out of 100 student in her poll are women. What type of sampling procedure is Janice using