What Stratified sample is
A stratified sample is a method of sampling that involves dividing a population into smaller groups known as strata, based on certain characteristics. The strata are then sampled independently, meaning that a separate sample is taken from each stratum. This type of sampling is used when researchers want to ensure that each subgroup of the population is adequately represented in the sample.
The steps for stratified sampling are as follows:
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Identify the population of interest.
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Divide the population into subgroups, or strata, based on characteristics such as age, gender, income level, etc.
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Calculate the desired sample size for each stratum.
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Select a sample from each stratum. This can be done using random sampling or by other means.
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Combine the samples from each stratum to create a single stratified sample.
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Analyze the data collected from the stratified sample.
Examples
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Stratified sampling can be used to ensure that a survey is representative of a population with different demographic characteristics, such as age, gender, race, and income.
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Stratified sampling can be used to ensure that a clinical trial is representative of a population with different levels of risk factors, such as age, gender, and health status.
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Stratified sampling can be used to ensure that a market research survey is representative of a population with different levels of purchasing power, such as age, gender, and income.
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Stratified sampling can be used to ensure that a study on customer satisfaction is representative of a population with different levels of customer loyalty, such as age, gender, and frequency of use.