For each of the following examples, identify the sampling method (random sampling from a process, stratified random sampling, systematic sampling, or cluster sampling)

For each of the following examples, identify the sampling method (random sampling from a process, stratified random sampling, systematic sampling, or cluster sampling).

a. In a study of bank loans to small businesses, a random sample of banks is selected. For the banks in the sample, data are collected on every small business loan approved during a particular month.

b. In a study of managers at a large firm, managers are categorized into three groups according to their division (field, production, or corporate). A simple random sample is taken from each group, and data are collected on each manager in the sample.

c. An economist is selected at random from the first 1,000 economists listed in an online directory of members of the American Economic Association. Every 1,000th economist thereafter is included in the sample.

d. Clients arriving at a free income-tax preparation service check in with a receptionist who collects basic information about them. Whenever a client has a February or an August birthday, the next client to check in is included in the sample.