In Figure 1a, we simulated the samples so that each error bar type has the same length, chosen to make them exactly abut. The importance of distinguishing the error bar type is illustrated in Figure 1, in which the three common types of error bars-standard deviation (s.d.), standard error of the mean (s.e.m.) and confidence interval (CI)-show the spread in values of two samples of size n = 10 together with the P value of the difference in sample means.
