Categorize the type of sampling (simple random, stratified, systematic, cluster, or convenience) used in each of the following situations.
(a) To conduct a pre-election opinion poll on a proposed amendment to the state constitution, a random sample of 10 telephone prefixes (first three digits of the phone number) was selected, and all households from the phone prefixes selected were called.
(b) To conduct a study on depression among the elderly, a sample of 30 patients in one nursing home was used.
(c) To maintain quality control in a brewery, every 20th bottle of beer coming off the production line was opened and tested.
(d) Subscribers to the magazine Sound Alive were assigned numbers. Then a sample of 30 subscribers was selected by using a random-number table. The subscribers in the sample were invited to rate new compact-disc players for a “What the Subscribers Think” column.
(e) To judge the appeal of a proposed TV sitcom, a random sample of 10 people from each of three different age categories was selected and those chosen were asked to rate a pilot show.