Source: Pulse Rate Graph; Public Domain http://wikimediafoundation.org/wiki/File:Pulse_Rate_Error_Bar_By_Exercise_Level.png
The test statistic in an ANOVA test. It is the ratio of the variability between the samples to the variability within each sample. If the null hypothesis is true, the F statistic will probably be small.
A hypothesis test that allows us to compare three or more population means.