Sampling, reliability & validity
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Flip to reveal answersWhat is the difference between a population and a sample?
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Question
What is the difference between a population and a sample?
Answer
The population is every individual of interest; the sample is the subset you actually collect data from. A good sample mirrors the population.
Question
Define simple random sampling.
Answer
Every member of the population has an equal chance of selection (e.g. names drawn from a hat, or GDC random numbers).
Question
Define systematic sampling.
Answer
Order the population, choose a random start, then pick every kᵗʰ member down the list.
Question
How do you find a stratified sample count for one group?
Answer
(group size ÷ population size) × sample size. Each stratum is sampled in proportion to its size.
Question
How do quota and stratified sampling differ?
Answer
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.
Question
Why is convenience sampling risky?
Answer
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.
Question
What does reliability mean for a test or measure?
Answer
Consistency — repeating the measurement gives (almost) the same result each time (small random error).
Question
What does validity mean for a test or measure?
Answer
It measures what it is supposed to measure, with no systematic bias. A measure can be reliable yet still invalid (consistently wrong).
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Topic 4.12 hub
Data collection & validity (HL only)
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