Problem-Solving and Data AnalysisEasy–MediumMargin of error from an interval
Problem-Solving and Data Analysis practice question
A poll based on a random sample reports that support for a proposal is between 45% and 51%, at a 95% confidence level. What is the margin of error, in percentage points?
Answer: 3
The interval runs from 45 to 51, a width of 6 points. The margin of error is half the width: 3 points (the estimate is 48% ± 3).
Common wrong answers
- If you answered 6
- 6 is the full width of the interval; the margin of error is the distance from the centre to either end.
- If you answered 48
- 48 is the centre of the interval — the sample estimate — not the margin.
- If you answered 51
- 51 is the upper end of the interval.
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