I guess you just didn't know. But even if you calculated the mean of all downward movements, it would still be pretty much useless for anything practical. You could get a higher value for your "downward volatility" with the price going up and vice versa. The fact that it was higher a year ago tells you essentially nothing in respect to actual price behavior. In effect, anything involving averages is practically useless and meaningless beyond normal distribution...

And alas, market prices do not belong there


Then you should have known that your reference to statistical significance was meaningless. Essentially, statistical significance shows how a certain data set refers to a given population that data set is drawn from. How your formula (or results obtained through it) can have "statistical significance" is beyond my imagination...