AQA · Mathematics · 8300
GCSE Maths: Sampling: stratified
Statistics · AQA GCSE Maths (8300). Cards are generated from the Corbettmaths textbook exercise and practice questions for Sampling: stratified (Corbettmaths Video 281), and every card links back to the exact page it came from. Practice tests are drawn from this deck’s own cards. Source material © Corbettmaths — used with attribution.
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What is a stratified sample?
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A sampling method where the population is divided into groups (strata) and a proportional sample is taken from each group.
Why is it appropriate to take a stratified sample when surveying students about a school library?
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To ensure all year groups are proportionally represented in the sample, as different year groups may have different library usage patterns.
In stratified sampling, if the total population is 200 and you want a sample of 50, what fraction of each stratum should you sample?
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50/200 = 1/4 (or 25%) of each stratum.
If a vet treats 100 pets and needs a stratified sample of 10, how many pets from a stratum containing 30 animals should be selected?
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3 pets. Calculate (30/100) × 10 = 3.
In stratified sampling, the sample from each stratum is ? to the size of that stratum in the population.
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proportional
What is the formula to calculate the number of items to sample from a stratum in stratified sampling?
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(Size of stratum / Total population) × Sample size
In stratified sampling, what are the groups into which the population is divided called?
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Strata (singular: stratum).
A school has 240 students and wants a stratified sample of 48. If 100 students travel by bus, how many bus users should be in the sample?
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20 students. Calculate (100/240) × 48 = 20.
Why might you stratify a sample by multiple characteristics (e.g., year and gender)?
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To ensure the sample accurately represents the population across multiple important dimensions that might affect the variable being studied.
After calculating stratified sample sizes, what additional step ensures randomness within each stratum?
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Randomly select the calculated number of individuals from each stratum (e.g., using random number generation or drawing names).
Why might you stratify a sample by vehicle type when surveying dealership customers?
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To ensure the sample represents the different types of vehicles sold in the correct proportions, giving more accurate overall results.
If you know the sample size for one stratum in a stratified sample, how can you find the total sample size?
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Divide the known stratum sample by (stratum population ÷ total population).
What is the main advantage of using stratified sampling over simple random sampling?
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It ensures all important subgroups are represented proportionally, reducing sampling error and improving representativeness.
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