Sampling & reliability
Practice Flashcards
What is a population (in statistics)?
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All Flashcards in Topic 4.1
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4.1.19 cards
What is a population (in statistics)?
Every individual or item you want to know about — the whole group the study is about.
What is a sample?
The part of the population you actually collect data from.
What is a census?
Data collected from the whole population (everyone).
Give one reason to sample instead of taking a census.
It is cheaper, faster, or the test is destructive (so a census is impossible).
When is a sample reliable?
When it represents the population — chosen fairly and large enough.
What is a biased sample?
One that over- or under-represents part of the population, so its results don't generalise.
Is a bigger sample always better?
A larger sample helps only if it is chosen fairly; a huge but unfair sample is still biased.
Give a situation where a census is impossible.
Destructive testing — e.g. measuring how long bulbs last, which destroys each bulb tested.
Difference between a parameter and a statistic?
A parameter describes the population; a statistic is calculated from a sample and estimates the parameter.
4.1.29 cards
Name the five sampling techniques.
Simple random, systematic, stratified, quota, convenience.
What is simple random sampling?
Every member of the population has an equal chance of being chosen (e.g. drawing lots or random numbers).
What is systematic sampling?
Order the population and take every k-th member after a random start.
How do you find the interval k for systematic sampling?
k = population size ÷ sample size.
What is stratified sampling?
Split the population into groups (strata) and sample each in proportion to its size.
How many do you take from a stratum?
(group size ÷ population) × sample size.
What is quota sampling?
Fill fixed numbers from each group, but choose the members non-randomly.
What is convenience sampling?
Choose whoever is easiest or first available.
Which techniques are most prone to bias, and why?
Quota and convenience — the members are not chosen randomly, so the sample is often unrepresentative.
Topic 4.1 study notes
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