Grizzly Bear Attacks in the USA/Data
Exposure
| exposure_level | exposure_days | daily_encounter_rate | injury_given_encounter | fatality_given_injury |
|---|---|---|---|---|
|
1 day |
1 |
0.00000534 |
0.048 |
0.13 |
|
10 days |
10 |
0.00000534 |
0.048 |
0.13 |
|
100 days |
100 |
0.00000534 |
0.048 |
0.13 |
The number of days represents the exposure duration in grizzly bear country. The daily encounter rate (0.00000534 or 5.34e-6) is calculated as 564 close encounters divided by 105.6 million visits in Yellowstone from 1991-2022. Injury given encounter (0.048) is 27 injuries divided by 564 close encounters. Fatality given injury (0.13) is averaged from 13.1% fatality rate in North American brown bear attacks (24 fatalities / 183 attacks, 2000-2015). These values are constant across rows as they represent base rates.
- Grizzly bear and American black bear interactions with people in Yellowstone National Park
- Brown bear attacks on humans: a worldwide perspective
Location
| location | location_odds_ratio |
|---|---|
|
Alaska |
3.0 |
|
Yellowstone National Park |
0.4 |
|
Glacier National Park |
1.0 |
|
Other Lower 48 States |
0.5 |
|
Non-Grizzly Area |
0.0 |
Odds ratios are scaled relative to Glacier National Park (baseline = 1.0) based on attack frequency and estimated exposure from studies. Alaska has higher odds (3.0) due to 51 attacks (2000-2015) and high bear density. Yellowstone's lower odds (0.4) reflect adjusted rates from 29 attacks and high visitation. Other states have lower odds due to fewer grizzlies.
Activity
| activity | activity_odds_ratio |
|---|---|
|
Hiking/Camping |
1.0 |
|
Hunting |
2.0 |
|
Working Outdoors |
1.0 |
|
Other Activities |
0.5 |
Odds ratios are scaled relative to hiking/camping (baseline = 1.0). Hunting has higher odds (2.0) based on 22% of attacks occurring during hunting (2000-2015), considering stealth and attractants increase risk. Working outdoors is similar to baseline, other activities lower.
Season
| season | season_percentage_attacks | season_months |
|---|---|---|
|
Summer |
48 |
3 |
|
Other Active Months |
52 |
6 |
|
Hibernation Season |
0 |
3 |
Percentage of attacks by season is verbatim from worldwide brown bear attack data (2000-2015). Number of months is used to normalize daily risk, assuming 9 active months total.
Precautionary Measures
| precautions | encounter_risk_reduction | precautions_risk_reduction |
|---|---|---|
|
Bear Spray and Food Storage |
0.5 |
0.08 |
|
Bear Spray Only |
1.0 |
0.08 |
|
Food Storage Only |
0.5 |
1.0 |
|
No Precautions |
1.0 |
1.0 |
Risk reduction multiplier represents the remaining risk after precautions. Bear spray alone reduces injury/death risk to 0.08 (92% effectiveness). Food storage alone reduces to 0.5 based on reducing food-related attacks.
RiskModel: Grizzly Bear Attacks in the USA/Data:EncounterInjuryFatality
Sorted Parameters:
encounter_risk = {daily_encounter_rate} * {exposure_days} * {location_odds_ratio} * {activity_odds_ratio} * ({season_percentage_attacks} / {season_months}) / (100 / 9) * {encounter_risk_reduction}
injury_risk = {encounter_risk}*{precautions_risk_reduction} * {injury_given_encounter}
fatality_risk = {injury_risk} * {fatality_given_injury}
Content: Your chance of having a dangerous, close encounter with a grizzly bear is {{One_In_X|{{#expr: {encounter_risk} }}|compare=RiskLadder }}.
Your chance of being injured in a grizzly bear attack is {{One_In_X|{{#expr: {injury_risk} }}|compare=RiskLadder }}.
Your chance of being killed in a grizzly bear attack is {{One_In_X|{{#expr: {fatality_risk} }}|compare=Micromorts }}.
The 100/9 factor in the encounter risk is because 100% of the attacks occur in the 9-month active season (not the 3 months the bears are hibernating).