a Which of the types of samples requires dividing a population into smaller groups?
B
b Notice that some counties have much larger populations than the others
A
a Stratified sample
B
b See solution.
Practice makes perfect
a We are told that to predict the results of a statewide election in New Mexico before all votes are counted, we conduct a poll. We also know that we ask 50 voters in each of the state's 33 counties as they leave the polls. To identify the type of sample used in this situation, let's recall all of the types of samples.
We divide population into groups randomly. Members in one or more of the groups — clusters — are selected.
Since we divided voters by their counties and then ask randomly 50 voters from each county, the described sample is a stratified sample.
b On the diagram we can see that some counties have larger populations than the others. Since we did not consider this fact and ask the same number of voters in each county, the sample can be a biased. To avoid that we could choose numbers of voters to ask to be proportional to the county's population.
