Sampling

A researcher sets out to determine the share of time the urban population of the United States listens to dance music. He identified the following population groups: construction workers, gym-goers, bar and night club patrons, and library readers.

1. What is the name for all those population subgroups?
2. What should the researcher ensure within each group and across his sample to preserve randomness?

Now the researcher changes his strategy in favor of pestering passers-by about their musical preferences in downtowns of Milwaukee, Cleveland, and St. Louis.

1. What type of population subgroup are Milwaukee, Cleveland, and St. Louis relative to the urban population of the United States?
2. What condition ensures that these three groups constitute a random sample of the US music listeners?