Variations Can Be Turned Into Proportions (Effect Size)
Here's the deal - if you know the total variance - you can determine what percentage of the total variance is related to the Between-Groups variance as compared to the Within-Groups Variance. The concept is similar to r² in discussions of the Correlation Coefficient.

That really means:
Of the total ways that people can vary from the population mean - what proportion of it is predictable from the Independent Variable (Our treatment - α) and what proportion is due to individual error or unknown variance (stuff we didn't control for or you personally - ε)?

There are different methods to do this. Many folks like a coefficient called Omega² the best. Another popular one is Eta² Most advanced statistics books have this formula.

You may be interested that for our data, Eta² is .91, which means 91% of the variance is due to our Independent Variable (Year in College).