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

In this scenario, Frank is dividing the population (residents of the state) into groups (towns) and then randomly selecting entire groups (12 towns) to collect data from all residents within those selected towns. This method is known as **cluster sampling**. Here's a breakdown of the options: 1. **Stratified sampling**: This involves dividing the population into subgroups (strata) and then randomly sampling from each stratum. Frank is not sampling from each town but rather selecting entire towns. 2. **Systematic sampling**: This involves selecting every nth individual from a list or population. Frank is not using this method. 3. **Cluster sampling**: This is the correct answer. Frank divides the population into clusters (towns) and randomly selects entire clusters to study. 4. **Convenience sampling**: This involves selecting individuals who are easiest to reach. Frank's method is not based on convenience but on random selection of towns. Thus, the type of sampling used by Frank is **cluster sampling**.