Margin of Error Math Example 2
Follow the full solution, then compare it with the other examples linked below.
Example 2
mediumA news report claims: 'The margin of error for this poll is ±3%.' Explain three things a careful reader should know about this margin of error.
Solution
- 1 Thing 1: The ±3% applies to the point estimate — actual support could be anywhere from (result-3%) to (result+3%)
- 2 Thing 2: It corresponds to a confidence level (usually 95%) — there's still a 5% chance the true value is outside this range
- 3 Thing 3: The margin of error only accounts for random sampling error — systematic errors (bias, non-response) are NOT included in the ±3%
Answer
(1) It defines a plausible range. (2) It assumes 95% confidence. (3) It doesn't account for non-sampling errors (bias).
Margin of error is widely reported but frequently misunderstood. It captures only random sampling variability — bias from non-random sampling, question wording, or response errors is separate. The confidence level is also usually omitted from media reports.
About Margin of Error
The maximum expected difference between the sample statistic and the true population parameter; it is half the width of a confidence interval.
Learn more about Margin of Error →More Margin of Error Examples
Example 1 easy
A poll of [formula] voters finds [formula] supporting a candidate. Calculate the margin of error at
Example 3 easyA 95% CI for average commute time is [formula] minutes. What is the margin of error, and what does i
Example 4 hardTwo polls: Poll A ([formula]): margin of error ±10%. Poll B ([formula]): margin of error ±2.5%. By w