To conduct a preelection 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.

To conduct a preelection 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 "cluster sample".

Explanation:

A selection method which is applied in statistical populations where socially unified but internally diverse categories are obvious, understood as cluster screening. It is also used in studies into marketing. The total population is separated into those groups in this sampling program and a simple random selection of the groups is chosen.

For an instance, in a class of total strength, one need to analyse the interest of students for science and arts individually, so the group is divided accordingly in class, after separation the quality of knowledge art and science student carry is tested by simple random selection from such divisions.

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