To study the mean respiratory rate of all people in his state, Frank samples the population by dividing the residents by towns and randomly selecting 12 of the towns. He then collects data from all the residents in the selected towns. Which type of sampling is used? Stratified sampling Systematic sampling Cluster sampling Convenience sampling

Frank is using cluster sampling! In this approach, he divides the entire population into groups (or clusters) - in this case, towns - and then randomly selects some of those clusters to include in the study. By collecting data from all residents within the chosen towns, he captures a more comprehensive picture of the respiratory rates within those specific clusters. As for a common mix-up, many people often confuse cluster sampling with stratified sampling. In stratified sampling, you would first divide the population into distinct subgroups (strata) and then randomly sample from each of those groups. Remember, cluster sampling focuses on entire groups, while stratified sampling targets specific segments within those groups!