A narrow survey margin of error does not rule out coverage or response bias

Sampling error arises because a sample is observed instead of the full population. Standard errors and associated confidence intervals quantify this component under the survey's assumptions. Nonsampling errors include missed population groups, nonresponse, incorrect answers, and collection or processing mistakes.

Illustrative example: a survey of event attendees receives thousands of answers but excludes people who left early. Its estimate can be numerically precise for respondents while missing a systematically dissatisfied group. Increasing the response count from the same incomplete frame does not establish that the omitted group resembles those observed.

When comparing surveys, inspect the target population, sampling frame, recruitment, response process, weighting, wording, and uncertainty calculation. Ask which errors the published interval actually represents. A smaller interval is useful evidence about precision, not a general certificate of accuracy.

The distinction matters before using a poll or satisfaction survey to describe a broader group. Diagnosing the direction or size of bias usually requires additional evidence; its possibility alone does not prove that an estimate is wrong.

Evidence status: source-based synthesis. Examples are illustrative; no new experiment or independent outcome verification is claimed.