A psychologist is studying sleep patterns of 3960 students at her university. She decides to start by asking 30 students how many hours of sleep they get on weekday nights. Identify the type of sampling in each of the below scenarios.
a) The psychologist assigns each student a number from1 to 3960. She selects the sample by randomly choosing one of the first 132 numbers and every 132nd number thereafter.
b) The psychologist assigns each student a number from 0001 to 3960 and uses a computer to randomly generate a list of 30 numbers to select the students for the sample.
c) Students are listed by the neighborhood they live in. The psychologist randomly selects six neighborhoods and then selects all within that neighborhood.
d) An equal proportion of students are randomly selected from each discipline.