Sampling methods

Overview

Target populations and representative samples, random, opportunity, systematic and stratified sampling with their strengths and weaknesses, and sampling bias.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is the difference between a target population and a sample?

   Model answer

   A target population is the whole group a researcher wants to find out about. A sample is the smaller group from that population who actually take part.

2. 2

   Why do researchers study a sample rather than the whole target population?

   Model answer

   A target population is usually too large for everyone to be tested. A sample saves time and money.

3. 3

   What is a representative sample?

   Model answer

   A representative sample contains the same kinds of people as the target population, in similar proportions. Findings from a representative sample can be generalised to that population.

4. 4

   Describe how to select a random sample.

   Model answer

   Every member of the target population is listed and given a number. The researcher then picks numbers by chance, such as with a random number generator.

5. 5

   Give one strength and one weakness of random sampling.

   Model answer

   Random sampling is unbiased, because every member of the population has an equal chance of being chosen. A complete list of the target population is often hard to obtain.

6. 6

   Why might a random sample still be unrepresentative?

   Model answer

   Chance alone can produce a sample that over-represents one group, such as mostly boys. The risk is greatest when the sample is small.

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