Analysis of variance, often shortened to ANOVA, is a series of statistical methods used to measure the statistical significance of the difference between groups. It was developed by Ronald Fisher, an extremely gifted statistician, who also popularized significance testing through his work on biological testing.

Our tests, using the z-statistic and t-statistic, have focused on sample means as the primary mechanism to draw a distinction between the two samples. In each case, we looked for a difference in the means divided by the level of difference we could reasonably expect and quantified by the standard error.

The mean isn't the only statistic that might indicate a difference between samples. In fact, it is also possible to use the sample variance as an indicator of statistical difference.

To illustrate how this might work, consider the preceding diagram. Each of the three groups on the left could represent samples of dwell times for a specific page with its own mean and...