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A credible poll is one whose sponsor, target population, sampling and recruitment methods, questions, field dates, weighting, and uncertainty are disclosed well enough to judge what its results can support. Sample size and margin of error matter, but neither alone proves that a poll represents the people it claims to describe.

Start with the poll’s purpose and people

Before weighing the headline result, identify who conducted the poll, who paid for it, and whom it is intended to represent. A poll of registered voters, for example, does not automatically describe all adults. Check whether the reported result covers the full sample or a subgroup, and note the size of that subgroup.

The American Association for Public Opinion Research (AAPOR) recommends checking the pollster and sponsor, including whether the sponsor may have an interest in the issue. A poll release should also identify its target population and explain how the people surveyed were selected or recruited. See AAPOR’s Transparency Initiative checklist.

Check how people entered the sample

A probability sample is drawn using a design in which each person in the target population has a known, non-zero chance of selection. A nonprobability sample may instead rely on opt-in panels, volunteers, or other recruitment without known selection probabilities. These are different designs, and the distinction affects what claims about precision are justified.

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For a probability sample, look for the sampling frame or list, who supplied it, which parts of the population it covers or excludes, and how participants were contacted or selected. For an online panel, check whether participants were recruited through probability sampling or opted in. A vague description such as “online survey” does not tell you enough about how respondents were obtained.

Interpret sample size in context

More completed interviews can reduce the sampling component of uncertainty, all else being equal. But a large sample cannot automatically fix a frame that misses parts of the target population, systematic nonresponse, leading questions, or unsuitable weighting. AAPOR cautions that a larger sample is not necessarily better when the design and coverage are weak.

There is no universal minimum sample size that makes a poll credible. The number needed depends on the target population, sampling design, desired precision, and whether the poll reports subgroups. Subgroup results rest on fewer interviews than the headline total and can be substantially less precise. Check the base for the specific result you want to use, not just the overall sample count.

Ask what the margin of error measures

A conventional margin of sampling error is associated with probability sampling. It describes sampling-related uncertainty under the stated design and assumptions; it does not account for every way a poll can go wrong. Coverage problems, nonresponse, question wording, measurement, and other design features can affect results too.

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When a poll reports a margin of error, check the confidence level and whether the calculation accounts for design effects from weighting, clustering, or other features. AAPOR’s journalist guide explains the familiar 95% confidence interval, but that is a general explanation—not proof that every poll uses that confidence level. See AAPOR’s journalist guide to polling.

Do not accept a conventional margin of error at face value for an opt-in or other nonprobability sample. Some such polls report a model-based “credibility interval.” That measure depends on modeling choices and assumptions used to connect respondents to the target population; it is not interchangeable with a probability-sample margin of sampling error. AAPOR’s statement on credibility intervals explains the distinction.

Inspect weighting and response-rate information

Weighting adjusts respondents’ contributions to the result. It may account for unequal selection probabilities or align measured sample characteristics with population benchmarks. A transparent report should name the variables used, the benchmark sources, and how weights were calculated. Weighting can improve alignment on measured characteristics, but its presence does not establish that unmeasured differences or other biases are absent.

A low response rate is a reason to examine recruitment and nonresponse, not a verdict that a poll is biased. AAPOR says response-rate information alone cannot determine how much nonresponse error exists—or even whether it exists. Read it alongside sample dispositions, coverage, and recruitment details. AAPOR’s standard definitions provide context for response rates and survey outcomes.

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Read the questions, mode, and field dates

  • Question wording and answer choices: Read the exact wording, not just a news summary. Look for clear, balanced phrasing, comparable treatment of competing positions, and any preceding introduction or question order that could shape responses.
  • Mode and language: Note whether interviews were conducted online, by phone, by text, in person, or through mixed modes, and which languages were used. Different modes can produce different results.
  • Field dates: Check when interviews took place. A poll is a snapshot of that period, and events during or just before fieldwork may matter to interpretation.

Look for data-quality disclosures

Useful methodology notes explain relevant checks used to identify invalid or unreliable responses. These may include attention and logic checks, screening for bots or fabricated profiles, prevention of repeat participation, and review of data processing. A report should make the checks relevant to its design understandable rather than using “quality controlled” as an unexplained assurance. AAPOR’s disclosure checklist includes these kinds of methodological details.

Compare polls on a like-for-like basis

When two polls disagree, a real change in opinion is one possible explanation; different methods can also shift estimates. Compare the details that define what each poll measured and how it measured it:

  • Target population and whether the result is for all respondents or a subgroup.
  • Probability or nonprobability design, recruitment, and frame coverage.
  • Field dates, mode, language, exact question wording, and response options.
  • Overall and subgroup sample sizes, weighting variables, and benchmarks.
  • Precision measure, its assumptions, and treatment of design effects.

A comparison is less informative when one report omits its frame, fails to say whether a panel is opt-in, or describes coverage only in vague terms. For election polls specifically, AAPOR’s journalist guide says a candidate usually needs to lead by 1.5–2 times the margin of sampling error for the lead to be statistically significant. That is election-specific guidance, not a universal rule for comparing every pair of polls.

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