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Planning an Investigation

FoundationHigherAQAEdexcel

Practise Planning an Investigation for GCSE Statistics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA and Edexcel. Good planning considers the population, sample size and constraints such as time, cost, ethics and confidentiality.

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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.

Foundation

WorksheetFoundation · PDFMark SchemeFoundation · PDF

Higher

WorksheetHigher · PDFMark SchemeHigher · PDF

Topic overview

Planning an investigation means deciding in advance exactly what data is needed, how it will be collected, and how it will be analysed.

The key decisions are: what population is being studied, whether to use a census or a sample, what sampling method to use, what size the sample should be, and what variables to measure. Each decision should be justified rather than simply stated.

A good plan also identifies practical constraints. Time, cost and access to the population all limit what is possible, and a plan that ignores them is not realistic. Considering possible sources of bias at the planning stage is far more effective than discovering them afterwards.

Revision notes

The key decisions

Define the population being studied. Decide between a census and a sample.

Choose a sampling method and justify it. Decide the sample size. Identify which variables to measure and how. Each decision needs a reason, not just a statement.

Practical constraints

Time, cost and access to the population limit what can be done.

A census may be ideal but impractical for a large population. A larger sample is more reliable but takes longer and costs more. Good plans acknowledge these trade-offs explicitly.

Anticipating bias

Think about who might be excluded by the chosen method before collecting any data.

Surveying only at a bus stop excludes drivers; surveying online excludes those without internet access. Identifying these problems at the planning stage allows the method to be improved.

Key points

  • Define the population being studied.
  • Decide between a census and a sample.
  • Choose and justify a sampling method.
  • Decide the sample size.
  • Consider time, cost and access.
  • Anticipate sources of bias before collecting data.

Worked examples

Example 1

A student wants to investigate how far students travel to school. State one decision they must make at the planning stage. [1 mark]

Working

Whether to survey every student or take a samplename a planning decision

Example 2

Give two practical constraints that may affect an investigation. [2 marks]

Working

The time available to collect and process the datagive the first constraint
The cost of carrying out the investigation, or difficulty accessing the populationgive the second constraint

Example 3

Explain why possible sources of bias should be considered before data is collected. [2 marks]

Working

Bias identified beforehand can be removed by changing the methodstate the benefit
whereas bias discovered afterwards means the data is already unreliable and must be recollectedexplain the consequence otherwise

Common mistakes

  • Stating decisions without justifying them.

    Questions usually ask why a choice is suitable, not just what it is.

  • Ignoring practical constraints.

    Time, cost and access all limit what is realistic.

  • Forgetting to define the population.

    Without a clear population, the sample cannot be judged.

  • Leaving bias until after collection.

    It is far easier to prevent bias than to correct for it afterwards.

Exam tips

  • Justify every planning decision you state.
  • Mention time, cost or access when evaluating a plan.
  • Define the population clearly.
  • Consider who the method might exclude.

Key terms

Population
The whole group being studied.
Census
Data collected from every member of the population.
Constraint
A practical limit such as time or cost.
Variable
A quantity being measured in the investigation.

Related topics

Written and reviewed against the current AQA and Edexcel specifications. Spotted an error? Let us know.