Null bar and null zone are better than the error bar to compare group means in graphs.
OBJECTIVE
Conventional graphs often include error bars around the group means. Regardless of what these bars depict, they are uninformative as to whether a difference between the groups is statistically significant.


METHODS
This article suggests plotting the null bar or null zone: that is, the range or area in which the means of the two groups fall if the null hypothesis of no difference cannot be rejected. The bar and zone are simply derived from the confidence interval around the difference, obtained from the t-test.
Boers
Maarten
M
Department of Clinical Epidemiology and Biostatistics, VU University Medical Center, PO Box 7057, 1007 MB Amsterdam, The Netherlands. keb.info@vumc.nl
D003626:Data Display; D003627:Data Interpretation, Statistical; D015233:Models, Statistical