AQA GCSE Statistics The collection of data: a complete overview of the enquiry cycle, data types and sampling

What this module demands

The collection of data is where every investigation begins. AQA tests whether you can plan an enquiry, classify data, choose a fair sample, design clear questions and recognise bias. Get these right and the rest of the course builds on solid foundations; get them wrong and every later calculation is suspect.

This guide walks through the five topics in specification order, then sets out the exam patterns AQA repeats. Each topic has a matching dot-point page with practice questions; this overview ties them together.

The statistical enquiry cycle

The module opens with the statistical enquiry cycle: plan and write a hypothesis, collect data, process and represent it, interpret and discuss, then evaluate and refine. It is drawn as a loop because evaluation feeds back into planning. A clear, testable hypothesis and a pilot study are central exam ideas.

Types of data

Types of data covers qualitative versus quantitative, discrete versus continuous, primary versus secondary, and categorical versus ranked. The data type controls which diagrams and averages are valid, so classification is a recurring first step.

Sampling methods

Sampling methods covers populations and sampling frames, census versus sample, and the random, systematic, stratified, quota and cluster methods. The stratified sample calculation, $\frac{\text{group size}}{\text{population}} \times \text{sample size}$, is examined almost every series.

Collecting data and questionnaires

Collecting data and questionnaires covers tally charts, open and closed questions, designing non-overlapping response boxes, and spotting leading or biased questions. Rewriting a faulty question or set of boxes is a classic exam task.

Controlling variables and bias

Controlling variables and bias covers explanatory and response variables, controlling extraneous variables, control groups and matched pairs, and the sources of bias. A fair test controls everything except the variable being investigated.

How this module is examined

A typical AQA profile for this module:

• The enquiry cycle. Naming the stages, writing a hypothesis, and explaining a pilot study.
• Data types. Classifying data and justifying the choice in context.
• Sampling. Describing methods and calculating a stratified sample.
• Questionnaires. Improving leading questions and faulty response boxes.
• Bias. Identifying sources of bias and how to reduce them.

Check your knowledge

A mix of recall and calculation questions covering this module. Attempt them under timed conditions, then check against the solutions.

1. State the five stages of the statistical enquiry cycle. (2 marks)
2. Is the number of pets a person owns discrete or continuous? (1 mark)
3. A school of $900$ has $300$ in Year 7. In a stratified sample of $60$, how many Year 7 students should be chosen? (2 marks)
4. Rewrite the response boxes "$0$ to $5$" and "$5$ to $10$" so they do not overlap. (2 marks)
5. Give one source of bias in a survey. (1 mark)
6. State one advantage of primary data over secondary data. (1 mark)
7. Name the sampling method that takes every $n$th item from a list. (1 mark)
8. In an experiment on fertiliser and plant height, name the response variable. (1 mark)