A 2008 academic paper on the effectiveness of bear spray. Of the 72 cases examined where people had used bear spray almost all escaped injury. There were only two cases involving polar bears, and in both cases, the spray worked.
More (Link)A 2020 10-page academic paper that looked for trends in ‘conflict bears’ in Churchill. the paper concluded that, “The number of conflict bears increased with the length of the ice-free period and there was a positive interaction between abundance and year on the number of conflict bears, indicating that when abundance was higher, the effect of year was higher.”
More (Link)