So this "study" that determines how effective bear spray is, only had data on 18 aggressive brown bear attacks?

"In 36% (18 of 50) of brown bear incidents, brown bears
acted aggressively towards people before being sprayed."

2 of those cases (out of 14 for which they had data), the pepper spray did not stop the bear. So in 15% of those cases, the spray did not stop the bear.

Be careful in trusting other people's statistics (or statistics in general). Read the data for yourself, draw your own conclusions, read the researchers conclusions, and see if/why they did or did not make the same conclusion as you.

Regardless, info on only 14 aggressive brown bear attacks does not give you enough info to draw a strong conclusion on whether or not bear spray will stop an aggressive brown bear. They should have mentioned their lack of data with regards to aggressive bears in their conclusion.