Quota, Cluster and Opportunity Sampling
Revise Quota, Cluster and Opportunity Sampling for GCSE Statistics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA and Edexcel. Quota, cluster, opportunity and judgement sampling are non-random methods, each with strengths and sources of bias.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA and Edexcel specifications. Every worksheet comes with a full mark scheme.
Topic overview
Three further sampling methods are used when a full sampling frame is unavailable or impractical.
Quota sampling sets a target number from each group and the interviewer selects people until the quota is filled. It needs no sampling frame and is quick, but the interviewer chooses who to approach, which introduces bias.
Cluster sampling divides the population into clusters, usually geographical, then randomly selects whole clusters and samples everyone within them. It is cheaper for spread-out populations but the clusters may not represent the whole population. Opportunity sampling, also called convenience sampling, simply uses whoever is available — the quickest method but the most likely to be biased.
Revision notes
Quota sampling
The interviewer is given a target number to survey from each group, and selects people until each quota is filled.
Advantage: no sampling frame needed, and it is quick and cheap. Disadvantage: the interviewer chooses who to approach, which introduces bias.
Cluster sampling
The population is divided into clusters, usually by area. Whole clusters are selected at random, and everyone within them is surveyed.
Advantage: much cheaper and quicker for populations spread over a wide area. Disadvantage: the chosen clusters may not be representative of the whole population.
Opportunity sampling
Also called convenience sampling. The sample is simply whoever is available at the time.
Advantage: the quickest and easiest method. Disadvantage: very likely to be biased, because the people available may not be typical of the population.
Key points
- Quota sampling fills targets for each group.
- Quota sampling needs no sampling frame.
- The interviewer's choice introduces bias.
- Cluster sampling selects whole groups at random.
- Cluster sampling is cheaper for spread-out populations.
- Opportunity sampling uses whoever is available.
Worked examples
Example 1
State one advantage of quota sampling. [1 mark]
Working
Example 2
Explain why opportunity sampling is likely to produce a biased sample. [2 marks]
Working
Example 3
Give one disadvantage of cluster sampling. [1 mark]
Working
Common mistakes
Confusing quota with stratified sampling.
Stratified uses random selection within each group; quota lets the interviewer choose.
Saying cluster sampling surveys some of each cluster.
Whole clusters are selected and everyone within them surveyed.
Saying opportunity sampling is unbiased because it is random.
It is not random — it uses whoever is available, which is a source of bias.
Giving only advantages.
Each method has a characteristic disadvantage that is examinable.
Exam tips
- Learn one advantage and one disadvantage of each method.
- Keep quota and stratified sampling clearly distinct.
- Link each disadvantage to a specific source of bias.
- Note which methods need no sampling frame.
Key terms
- Quota sampling
- Filling target numbers from each group by interviewer choice.
- Cluster sampling
- Randomly selecting whole groups and surveying all within them.
- Opportunity sampling
- Using whoever is conveniently available.
- Bias
- A systematic tendency to misrepresent the population.
Related topics
Written and reviewed against the current AQA and Edexcel specifications. Spotted an error? Let us know.