Incidence Rate Calculation
The incidence rate is 375 per 100,000 population per year.
Understanding the Calculation
The question presents a straightforward epidemiological calculation where you have:
- Population at risk: 100,000 people
- New cancer cases diagnosed: 300 + 75 = 375 cases
- Time period: One year
The incidence rate formula is: (Number of new cases / Population at risk) × 100,000
In this scenario: (375 / 100,000) × 100,000 = 375 per 100,000 per year
Context from Cancer Epidemiology
To put this rate in perspective using current cancer epidemiology data:
Global and Regional Comparisons
This calculated rate of 375 per 100,000 is substantially higher than most real-world cancer incidence rates. For comparison, global cancer incidence (including non-melanoma skin cancers) varies from approximately 97 per 100,000 in Western Africa to 508 per 100,000 in Australia/New Zealand among men, and from 103 per 100,000 in South-Central Asia to 411 per 100,000 in Australia/New Zealand among women 1.
In the United States, the overall cancer incidence rate is approximately 450-500 per 100,000 when including all cancer types, with rates declining by 1.8% annually in men during 2007-2011 while remaining stable in women 2.
In Europe, specific cancer incidence rates vary widely by cancer type: rectal cancer occurs at 15-25 cases per 100,000 per year 3, pancreatic cancer at 4.5-8.7 per 100,000 per year 3, and bladder cancer at an overall crude rate of 20.4 per 100,000 3.
Important Epidemiological Principles
Incidence rates are always expressed per standard population unit (typically per 100,000) and per time unit (typically per year) to allow meaningful comparisons across different population sizes 2, 1.
Age-standardized rates are preferred for comparing populations with different age structures, as cancer incidence increases dramatically with age—from 1.5 per 100,000 in those aged 15-44 years to 55 per 100,000 in those over 65 years for pancreatic cancer alone 3.