Which expression correctly represents the incidence rate formula given N as injuries, EH as total hours, and 200,000 as the base?

Which expression correctly represents the incidence rate formula given N as injuries, EH as total hours, and 200,000 as the base?

• A. (EH/N) x 200,000
• B. (N/EH) x 200,000
• C. (N/EH) x 100,000
• D. N x 200,000/EH

Answer: (B)

The quantity being measured is how many injuries occur per unit of exposure time, standardized to a base of 200,000 exposure hours. That means you take the number of injuries (N), divide by the total exposure hours (EH) to get injuries per hour, and then multiply by 200,000 to express the rate per 200,000 exposure hours. So the correct form is (N/EH) × 200,000. Inverting the ratio to EH/N would give hours per injury, not injuries per hour, which isn’t a rate of occurrences. Using a base of 100,000 would shift the standard from 200,000 hours to 100,000 hours, changing the normalization. The form N × 200,000 / EH is algebraically the same as (N/EH) × 200,000, so it yields the same rate, just written differently.

The quantity being measured is how many injuries occur per unit of exposure time, standardized to a base of 200,000 exposure hours. That means you take the number of injuries (N), divide by the total exposure hours (EH) to get injuries per hour, and then multiply by 200,000 to express the rate per 200,000 exposure hours. So the correct form is (N/EH) × 200,000.

Inverting the ratio to EH/N would give hours per injury, not injuries per hour, which isn’t a rate of occurrences. Using a base of 100,000 would shift the standard from 200,000 hours to 100,000 hours, changing the normalization. The form N × 200,000 / EH is algebraically the same as (N/EH) × 200,000, so it yields the same rate, just written differently.