To assess the presidential candidate preferences of the registered voters in Maricopa County, a researcher classifies the voters by social class and age. The researcher randomly selects voters from each subgroup according to its proportion in the entire county. This sampling technique is called sampling.

Stratified random

Explanation:

Stratified random  sampling is the technique through which population is split into small section which is called strata.This strata division of population is based upon shared characteristics of the population to draw probability sample from it .

According to the question, stratified random sampling is used by researcher for classifying voters into section of age and social class group division to randomly select voters from subgroup proportion.  

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