Error bar

Abar chartwithconfidence intervals(shown as red lines)

Error barsare graphical representations of the variability of data and used on graphs to indicate theerrororuncertaintyin a reported measurement. They give a general idea of how precise a measurement is, or conversely, how far from the reported value the true (error free) value might be. Error bars often represent onestandard deviationof uncertainty, onestandard error,or a particularconfidence interval(e.g., a 95% interval). These quantities are not the same and so the measure selected should be stated explicitly in the graph or supporting text.

Error bars can be used to compare visually two quantities if various other conditions hold. This can determine whether differences arestatistically significant.Error bars can also suggestgoodness of fitof a given function, i.e., how well the function describes the data. Scientific papers in the experimental sciences are expected to include error bars on all graphs, though the practice differs somewhat between sciences, and each journal will have its ownhouse style.It has also been shown that error bars can be used as adirect manipulation interfacefor controlling probabilistic algorithms for approximate computation.Error bars can also be expressed in aplus–minus sign(±), plus the upper limit of the error and minus the lower limit of the error.

A notorious misconception in elementary statistics is that error bars show whether a statistically significant difference exists, by checking simply for whether the error bars overlap; this is not the case.

See also

• Box plot
• Information graphics
• Model selection
• Significant figures