Margin of Error on LiveStories

LiveStories charts often display a margin of error. Many data sources—including the American Community Survey (ACS) and the Centers for Disease Control and Prevention (CDC)—provide data in the form of estimates, based on surveys. Such data therefore has a measure of uncertainty. The margin of error is a +/- range around each estimated value. It essentially shows how uncertain we should be about that value. The margin of error will generally be larger for places with small populations, since these places have a more limited sample size.

Margins of error have an associated confidence level—that is, the degree of confidence that the value actually falls within the error's range. Different sources use different confidence levels. The ACS, for example, uses a 90% confidence level, while the CDC uses a 95% level. LiveStories normalizes all margins of error to a 68% confidence level, or one standard deviation.

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The margin of error for this census tract’s ACS population estimate is +/-292.42 people, at a 68% confidence level.