Error bars within treatments illustrate confidence intervals, standard errors, standard deviations or other quantities. However, different types of error bars exist, so figure legends must be sure to distinguish which error bar is being represented.
Two common types of error bars exist: inferential and descriptive. Inferential error bars measure the mean of the variables presented as well as a range of values that, if calculated correctly, enable an individual to determine the true mean of the equation. Descriptive error bars show how data is spread as well as the average difference between the data points and their mean, usually displaying the lowest and highest values.