SCORE Mathematics
Definition
To choose a stratified random sample, divide the population into strata, groups of individuals that are similar in some way that is important to the response. Then choose a separate SRS from each stratum and combine these SRSs to form the full sample.
Example
A school official wants to estimate the average number of hours per week that students devote to homework. Because she believes that this figure will differ considerably among classes, stratified random sample will be employed. The population of students at this school will be group into four strata consisting of all freshman, sophomore, juniors and seniors. From each stratum, a random sample of students will then be selected. The resulting information can be combined to obtain an estimate that is expected to be more precise than that obtained from a random sample of the entire population.
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