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Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →A poll’s margin of error describes uncertainty from sampling—not every way a poll can miss the mark. A lead or change is meaningful only when the difference is supported by an appropriate statistical test and the polls are sufficiently comparable.
What a poll’s margin of error means
A poll asks a sample of people to stand in for a larger population. Another properly conducted sample could produce a somewhat different estimate. A margin of sampling error expresses the range associated with that sampling variation under a specified method and assumptions; it is not a guarantee that the population’s true value falls inside that range.
The margin covers sampling uncertainty, not the full set of ways a poll can be wrong. The American Association for Public Opinion Research (AAPOR) notes that nonresponse bias and an incorrect turnout model, for example, are outside the margin. A poll can report a narrow margin and still be affected by those or other measurement problems. See AAPOR’s Polling Accuracy explainer.
Describe poll movements in percentage points. A change from 48% to 51% is a 3-percentage-point increase; a 3% increase would describe a relative change and mean something different.
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Is a 2-point lead meaningful?
Not necessarily. The margin shown beside an individual candidate’s share is not automatically the uncertainty around the difference between two candidates. AAPOR illustrates the point with Candidate A at 48% and Candidate B at 46%, each with a margin of ±3 percentage points. Its explainer treats the 2-point lead as a statistical tie: the headline figures do not establish that A is ahead.
Pew Research Center gives a related example: when each candidate’s individual estimate has a 3-point margin, the uncertainty in the difference between the candidates is approximately 6 percentage points. The margin for the lead is therefore not simply the margin printed next to either candidate’s share.
For a claim that one candidate is statistically ahead, look for a pollster’s direct test or confidence interval for the difference, calculated using the survey design. Without that information, the point estimates alone do not establish a meaningful lead. AAPOR’s example is a rule-of-thumb illustration, not a universal substitute for a poll-specific test.
Did support really change, or is it within the margin of error?
To assess movement between two survey waves, the relevant question is whether the difference between the estimates is larger than expected from their uncertainty. A pollster-provided test or confidence interval for the difference is preferable; it should account for both estimates and the survey design. The Office for National Statistics describes significance testing as a way to assess whether a difference between survey estimates reflects population change rather than sample variation. It notes that a 5% threshold is often used, but statistical significance is not the same as practical importance.
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Do not treat visual overlap—or lack of overlap—between two separately reported margins as a definitive test unless the pollster’s method supports that interpretation. If the headline results do not provide the information needed to test the difference, say that the available figures do not establish that the change is statistically meaningful.
Even a statistically detectable change may be too small to matter in context. Conversely, a larger-looking movement can remain uncertain when the estimates are imprecise. “Statistically significant” describes the outcome of a suitable test; it does not by itself mean that a shift is consequential or that it will persist.
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Check whether the polls are comparable
A change in published numbers can reflect a change in the survey rather than a change in public opinion. Before comparing two results, check the following:
- Population and geography: Are both polls about the same group and area? Adults, registered voters, and likely voters are different populations.
- Field dates: Were the polls conducted at similar times? A later poll can reflect real events or campaign movement as well as sampling variation.
- Question and answer choices: Different wording or response options can produce different answers.
- Mode and recruitment: Compare how respondents were contacted and recruited, and how the sample was constructed.
- Sample size and subgroups: Smaller samples generally yield less precise estimates. A subgroup uses fewer respondents than the full sample, so its uncertainty is usually greater; AAPOR advises journalists to identify subgroup sample sizes.
- Weighting and design: Weighting, clustering, and other features of the sample design can affect estimates and their precision. Check whether reported uncertainty accounts for design effects.
- Test of the difference: Prefer a direct test or interval for the change over a comparison of point estimates alone.
AAPOR’s reporting and transparency guidance sets out methodological details that help readers evaluate these comparisons.
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Probability polls and opt-in samples do not support the same margin
Probability samples
When participants are selected through a probability design, a design-based margin of sampling error can be estimated. Real surveys may require adjustments for weighting, clustering, or other departures from a simple random sample. AAPOR recommends that reports say whether sampling-error estimates have been adjusted for design effects.
Nonprobability samples
Opt-in panels and other nonprobability samples do not have a simple conventional margin-of-error calculation. Any reported precision measure depends on a statistical model and its assumptions, which should be disclosed. AAPOR cautions that a “credibility interval” is not interchangeable with the conventional margin of sampling error used for probability polls. See its guidance on nonprobability sampling.
A poll is a snapshot, not an election forecast
A poll estimates opinion among a defined population during a particular period; it does not guarantee an election result. AAPOR’s 2024 pre-election guidance says polls can offer an approximate picture of where things stand but are not predictive, and may not identify who is ahead in a very close election. Read multiple polls and broader trends rather than treating one small movement as proof that the race has shifted.
That distinction also matters when interpreting past polling errors. AAPOR’s 2020 task-force report found that 223 of 348 state-level polls (64%) had a candidate margin more than twice the margin of error. Under that report’s standard, the other 36% could not statistically distinguish the margin from a tie. Those figures describe that particular set of 2020 polls; they are not a measure of current polls or a rule for predicting future elections.
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