One day the variance and the standard deviation were engaged in a heated argument over which was the better measure of variability.
The standard deviation shouted at the variance, "You are useless because you don't even relate to the original score scale."
The variance glared back and yelled, " Oh yeah! You are totally worthless because you are far too radical."
Just then the mean deviation stepped between the two indices and pushed them both back. In a proud voice the mean deviation proclaimed,"You are both wrong! I am ABSOLUTELY the best measure of variability since both of you would be worth ZERO if you didn't square your deviations!!!!"
*OK this may not bring down the house with laughter. I still have a place in my heart for the antiquated mean deviation because of its intuitive nature. I believe students can see a rationale for both S and S2 if MD is introduced first.
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