### error bar

(feature of a graph to indicate accuracy)

An **error bar** is a means by which uncertainties in
observations or calculations can be expressed.
It consists of a line segment crossing a point or
the top of a bar graph showing a range of values
around the indicated value. Similar bars are used for plots
of points, sometimes with bars along each axis.
The bar indicates that the plotted value is only the mean or the most
probable value, and the bar's length indicates some statistic regarding
distribution of either the measured values, the sample size,
or sources of error. Commonly used statistics for the bar:

**standard deviation** - to indicate distribution of observed data, basically showing where 2/3 of the data lies.
**confidence interval** (often 95% percent confidence interval but other percentages may be specified) - shows a range encompassing this percentage chance of including the mean.
**standard error of the mean** - indicates how well the sample represents an entire population.

A fourth usage of such bars, probably best not described as "error bars",
simply indicates the full range of data, i.e., marking the highest
and lowest value.

As a general rule, the shorter the error bar, the "better" or "more
significant", but each of the three types has its own formula and
shows as a different length based on the same data, suggesting
an indication of the type of error bar helps the viewer. The appropriate
choice of type/calculation depends upon the nature of the data and
what is being demonstrated.

(*statistics,graph*)
**Further reading:**

http://en.wikipedia.org/wiki/Error_bar

http://datanuggets.org/wp-content/uploads/2016/06/error-bars-points-of-significance.pdf

**Referenced by pages:**

gyrochronology

neutrino (ν)

standard siren

Index