Margin of Error & Poll Interpretation Lab
Draw samples from a population with a known true proportion and watch the margin of error narrow as the sample size grows. Then practice reading real poll scenarios to decide when a reported lead is meaningful and when it is just a statistical tie.
Guided Experiment: Watch the Margin of Error Shrink
Hypothesis
Setup
Run Experiment
Analyze
Conclude
Do you predict a bigger or smaller sample will give a poll estimate closer to the true population proportion?
Write your hypothesis in the Lab Report panel, then click Next.
Controls
Draw a Sample
Estimate vs. True Proportion
Sample estimate: 61.4% ± 4.3 points (95% confidence interval: 57.1% to 65.7%)
The shaded band is the estimate's margin of error. Increase the sample size to watch it narrow.
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Reference Guide
What Margin of Error Means
- It is a range, not a guarantee. A margin of error of plus or minus 3 points means the true value is very likely within 3 points of the reported number.
- Bigger samples narrow the range. Margin of error shrinks as sample size grows, roughly by one over the square root of n.
- A lead inside the margin is a tie. If two candidates are closer together than twice the margin of error, the race is a statistical tie.
- It does not fix a biased sample. Margin of error only measures random sampling variation. It says nothing about whether the people surveyed represent the full population.
How to Use This Lab
- In the Sampler panel, set a true proportion and a sample size, then resample to see the estimate change.
- Increase the sample size and watch the margin of error, and the shaded interval, narrow.
- Switch to Poll Cards to read a reported poll result and answer the interpretation question.
- Reveal each card to check your answer and read the explanation.
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