Who knows. it's a random unsubstatiated statistic. The bioligist types I've discussed it with seem to think it's effective. While 55% might be low, if it's that high, my personal unsubstantiated opnion is that I bet that's more effective than a handgun would be on average.

I have however been cautioned that polar bears appear to mostly unbothered by it - something about their taste and smell being different and relating to their nictating membranes and nose adapted for heading after things underwater. So the line I was fed from the bear people was basically the responsible (for the bear's well being) and prudent (for your well being) was to carry proper spray for "normal" bears - and if you valued your own butt carry a big gun in polar bear turf