# Write a research problem that would be best studied using a probability sample.

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A **probability sampling** is a method of investigation that uses a random sample. This type of random sampling ensures that all different categories in your study have the same probability of being chosen.

For example, a study that might use a probability sample is an investigation of voters' views about an election because the investigator will want to get a wide range of views and make sure that he or she is getting a random sample. Studies can use **simple random sampling** and assign all voters to what's called the sampling frame (the complete list of total subjects) and then have a computer pick out certain voters for interviewing. Another way to approach this study is to use **stratified random sampling**. In this method, the population is divided into certain categories, such as voters from ages 18-30, 31-50, 50-80, over 80, etc. The study would try to get the same number of people in each category to make sure the investigator is studying different sub-groups in the population and that the investigator can make subgroup comparisons. The study can also use **cluster random sampling**. In this method, the population is divided into clusters, usually by geographic region, and then the investigator chooses certain clusters or areas with the sample randomly. Within the chosen clusters (which might be counties), each town is sampled. For example, the study might look at voters within Massachusetts. Each county would be a cluster, and a few counties would be chosen. Within each county, voters in each town would be sampled. These are different methods of random sampling with a probability sample.