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Sampling

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  Edexcel IAL Statistics 3 (WST03)

Sampling

The big idea: Every sampling method trades cost and convenience against how representative the sample is.

Summary — What This Chapter Covers
  • Simple random sampling needs a sampling frame.
  • Systematic: every kth item from a random start.
  • Stratified: sample each group in proportion to its size.
  • Quota: like stratified but not random; opportunity: whoever is available.
1. Methods of Sampling
Methods

Choosing and describing a method

Exam answers need the method and how to carry it out: number the population, use random numbers, ignore repeats; for stratified sampling, calculate the number from each stratum.

Worked Example

A school has 300 Year 12 and 200 Year 13 students. How many of each should be in a stratified sample of 40?

Memorise
Random

Needs a sampling frame

Systematic

Every kth item

Stratified
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More Statistics 3 topics

Combinations of Random Variables
Linear combinations of normal variables
Methods of sampling
Unbiased estimates and standard error
Goodness-of-fit tests
Spearman's rank correlation
The central limit theorem
Contingency tables
Testing correlation coefficients
Estimation, Confidence Intervals and Tests