The national crime victimization survey selects subjects by identifying rural counties or metropolitan areas as primary sampling units, then chooses geographic regions within these units, and then chooses addresses within the geographic regions. this is an example of a sampling approach.

multi-stage cluster.

Explanation:

The National Crime Victimization Study identifies topics by choosing rural counties or urban areas as main sampling units, then selecting geographical areas within those units, and then selecting addresses within geographical areas. This is an illustration of a sampling method for a multi-stage cluster.

Multi-stage sampling may be a conceptual model of cluster sampling as it is a method of sampling involving the division of the demographic into groups (or clusters). Then  1 or more than 1 clusters are randomly selected and all of them are sampled within the selected cluster.

answer:

d. because dr. laguardia selected a widely used measure, his study generalizes to has strong external validity. external validity has limited external validity. other applications of this measure.

the widely used measure that he applied to his experiment was the benton facial recognition test. it employed on to football players and as result, only players who suffered brain concussions did not pas this test. and although it has an external validity, it is limited because it isn't general to apply to other population.

could you go a bit more in depth with you question? it's quite hard to understand. as soon as you do that i will be glad to : )