In 2003 there were 44,232 new AIDS cases in a mid-year population of 290,809,777. What is the incidence rate per 100,000?

1. Divide new cases by the mid-year population: 44,232 divided by 290,809,777 equals 0.0001521. 2. Multiply by 100,000 to get a readable figure. 3. 0.0001521 times 100,000 equals 15.21 new cases per 100,000 population. 4. 1.52 and 152.10 come from using 10,000 or 1,000,000 as the multiplier instead of 100,000. 5. 0.15 keeps only a multiplier of 1,000, so the rate is understated by a factor of 100. _Source: CDC Principles of Epidemiology in Public Health Practice (3rd ed., US federal, public domain), Lesson 3 "Measures of Risk", section Definition of incidence rate_