We encourage all persons with or without a firearm, to consider carrying a non-lethal
deterrent such as bear spray because its success rate under a
variety of situations has been greater (i.e., 90% successful for
all 3 North American species of bear; Smith et al. 2008) than
those we observed for firearms.
Seems like they have pretty decent confidence. And they never say "our study is likley wrong". They caveat it.
https://westernwildlife.org/wp-conte...-Deterrent.pdf