Reading statistical claims critically
Check denominators, comparison groups and the difference between association and cause.
Before you begin
- Percentages
- Evaluating sources
Ask what the number actually measures
A percentage needs a clear base and a defined outcome. An increase from 10 to 15 is a 50% increase, not an increase of 50 percentage points. If a proportion rises from 10% to 15%, it rises by 5 percentage points and by 50% relative to its initial value. Accurate wording prevents a small dataset from sounding more decisive than it is.
Look for alternative explanations
Two quantities can move together without one causing the other. Other variables, selection effects or chance may contribute. Ask whether there is a suitable comparison group, whether the samples are comparable and how the outcome was measured. Statistical evidence can support a cautious association even when it cannot support a causal claim.
Worked example
A headline says 'Club participation doubled' when membership rose from 4 to 8. Evaluate the wording.
Show the worked solution
- The relative change is correctly described as doubling.
- The absolute increase is four people, which provides useful scale.
- The headline alone does not explain why membership changed or whether the trend will continue.
The wording is numerically true but incomplete without the starting and ending counts.
Try it yourself
A survey finds frequent readers report higher grades. What can it establish by itself?
Common mistakes
- Do not interchange percentage change and percentage-point change.
What can you explain now?
A participation rate rises from 20% to 30%. State the percentage-point change and the relative increase.
Compare with the explanation
10 percentage points; a 50% relative increase.
Subtract the percentages for the point change. Divide the increase of 10 by the starting 20 to obtain 0.5, or 50%.
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Original StudyForA content. AI-assisted checks completed; subject-teacher review is still pending. These lessons are not endorsed by an exam board.
Common Core English language arts standards ↗