In a study of attitudes to university policies, a researcher chose initially 150 first-year students, 130 second-year students and 100 third-year students (N1=380). Then, the researcher chose 25 male and 25 female students from each year group who were finally interviewed (N2=150). The sampling procedure used in this study was
Probability sampling
—>> Multi-stage sampling
Stratified sampling
Maximum variation sampling
