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What is the difference between a population and a sample?
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All Flashcards in Topic 4.12
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4.12.18 cards
What is the difference between a population and a sample?
The population is every individual of interest; the sample is the subset you actually collect data from. A good sample mirrors the population.
Define simple random sampling.
Every member of the population has an equal chance of selection (e.g. names drawn from a hat, or GDC random numbers).
Define systematic sampling.
Order the population, choose a random start, then pick every kᵗʰ member down the list.
How do you find a stratified sample count for one group?
(group size ÷ population size) × sample size. Each stratum is sampled in proportion to its size.
How do quota and stratified sampling differ?
Both target groups in proportion, but stratified picks members randomly within each group, while quota lets the interviewer choose — so quota is non-random and can be biased.
Why is convenience sampling risky?
It surveys whoever is easiest to reach, so the sample is usually unrepresentative — it tends to over- or under-represent certain people, giving biased estimates.
What does reliability mean for a test or measure?
Consistency — repeating the measurement gives (almost) the same result each time (small random error).
What does validity mean for a test or measure?
It measures what it is supposed to measure, with no systematic bias. A measure can be reliable yet still invalid (consistently wrong).
Topic 4.12 study notes
Full notes & explanations for Data collection & validity (HL only)
Math AI exam skills
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