A bigger percentage does not always mean more people. Check the total each percentage describes.
A pie chart divides one total into shares. In the practice survey, each of 20 respondents chooses one main travel mode: 12 walk, 6 take the bus and 2 use a car. Walking is 12 / 20 x 100 = 60%; bus is 30% and car is 10%.
To draw a sector, multiply its fraction by 360 degrees. The angles are 216 degrees for walking, 108 for bus and 36 for car. Together they fill the circle.
This works because every respondent belongs to just one category. If people can choose several modes, the counts may exceed the number of respondents. They would no longer be separate shares of those people. Account for missing responses too.
Always check the total, or denominator, before comparing pies. In a second sample, 50% of 100 respondents walk. That is 50 walkers: more than the first sample's 12, despite the smaller percentage. Keep the question and sampling method comparable before treating two charts as evidence of change.
Step by step
Check the whole
Establish the total and whether each response belongs to exactly one category.
Calculate each share
Divide category count by total, then multiply by 100 for percent or 360 for degrees.
Compare carefully
A higher percentage can represent a smaller count if the total is smaller.
Worked example: A bigger share, but fewer people
The 20-person sample has the higher walking share: 60% rather than 50%. The 100-person sample has more walkers: 50 rather than 12. Use the comparison that answers the question.
Watch out for this
A 60% slice must contain more people than a 50% slice.
That follows only if the totals are the same. Multiply each share by its own denominator first.
Check your understanding
Which contains more walkers: 60% of 20 respondents or 50% of 100 respondents?
- 60% of 20, because 60 is larger than 50.
- 50% of 100, because it represents 50 walkers rather than 12.
- They must contain the same number because both are percentages.