The statistical enquiry cycle
- Every investigation follows the same cycle: plan, collect data, process and represent, analyse and interpret, then evaluate. The evaluation often leads to a new, better question, so the cycle starts again.
- Planning means choosing a question or hypothesis, deciding what data you need, where it will come from and how much you will collect.
Hypotheses
- A hypothesis is a statement that can be tested with data, such as "Year 11 students spend more time on homework than Year 9 students."
- A good hypothesis is specific and measurable. "Boys are better at sport" is too vague; "Boys run 100 m faster than girls in our school" can be tested.
- The results either support the hypothesis or don't. Statistics never prove it for certain.
Primary and secondary data
- Primary data is collected by you, for your purpose (surveys, experiments, observation). It is exactly what you need and you know how it was collected, but it takes time and money.
- Secondary data was collected by someone else (such as the Office for National Statistics, websites or newspapers). It is quick and cheap, but it may be out of date, biased or not quite what you need.
Problems to plan for
- Constraints: time, cost, ethical issues (such as upsetting people), confidentiality (keeping personal data safe) and getting access to people or data.
- A pilot study is a small trial run. It tests whether questions are clear and the method works, before the main investigation.
- Extraneous variables are other factors that could affect the results. Control them by keeping them the same, so the test is fair.
Key terms
- Hypothesis
- A statement that can be tested using data.
- Statistical enquiry cycle
- Plan, collect, process and represent, analyse and interpret, evaluate.
- Primary data
- Data you collect yourself for your own purpose.
- Secondary data
- Data collected by someone else.
- Pilot study
- A small trial run to test the method before the main investigation.
- Extraneous variable
- A factor other than the one being tested that could affect results.
- Constraint
- A limit on an investigation, such as time, cost or ethics.