On a graph of points representing means, a line through a point indicating the margin of error (see illustration). Error bars on a line graph or histogram may indicate confidence intervals, standard deviations, or standard errors of the means, standard errors frequently being preferred because they provide a visual guide to statistical significance: if two SE error bars overlap, then the difference between the two means is non-significant (at p < .05), whereas if they do not overlap, then the difference is usually significant. Compare box-and-whisker plot.
Error bar. Ther vertical lines through the four means represent standard errors of the means, suggesting that adults improved significantly but children did not.