Figure 1.

Many different distributions can lead to the same bar graph. The full data may suggest different conclusions from the summary statistics. The means and S.E. values for the four example datasets shown in b–e are all within 0.5 units of the means and S.E. values shown in the bar graph (a). p values were calculated in R statistical software (version 3.0.3) using an unpaired t test, an unpaired t test with Welch's correction for unequal variances, or a Wilcoxon rank sum test. In b, the distribution in both groups appears symmetric. Although the data suggest a small difference between groups, there is substantial overlap between groups. In c, the apparent difference between groups is driven by an outlier. d suggests a possible bimodal distribution. Additional data are needed to confirm that the distribution is bimodal and to determine whether this effect is explained by a covariate. In e, the smaller range of values for group 2 may simply be due to the fact that there are only three observations. Additional data for group 2 would be needed to determine whether the groups are actually different. var, variance. Adapted from Weissgerber et al. (14) under a creative commons license.