The Denver Area Big Organization for Medicine and Business (DA-BOMB) is a not-for-profit consultant group for area hospitals and medicine-related businesses. They survey patients discharged from...

The Denver Area Big Organization for Medicine and Business (DA-BOMB) is a not-for-profit consultant group for area hospitals and medicine-related businesses. They survey patients discharged from hospitals in the past year to construct patient satisfaction profiles. If the study design was to group the patients according to length of hospital stay (2 days or less, 3-7 days, 8-14 days, or more than 14 days) and then draw a random sample from each group, what kind of sampling procedure is used?