Question

Why is the first one simple random sample but the second one is not?

1. Jane wants to learn about the study behaviors of students in her STAT 303 class. She gets a class roster of all 52 students in the class and randomly selects 5 students to survey. Is this a simple random sample?

2. Rachel wants to determine whether or not hospital patients who have been discharged in the past week in her state are satisfied with the level of care they received during their stay. There are 74 hospitals in her state. She goes to each hospital and gets a list of all the patients who have been discharged within the past week. From each of these lists, she randomly selects 10 people (for a total of 740 people) and asks them about the care they received during their stay. Is this an example of a simple random sample?

Answer 1

In case of 1st problem Jane is selecting students from a class. There are total 52 students from which she is drawing 5 students randomly. As probability of selecting any particular student is same, therefore it's a case of simple random sampling.

In 2nd problem patients are categorized first wrt the hospital in which they had admitted. Then from each hospital she is drawing 10 sample randomly. Here we can see probability of selecting any particular patients within a perticular stratum(group) same. We can consider this case as simple stratified sampling.