Why is the infant mortality rate a ratio but not a proportion?

1. A proportion needs every unit in the numerator to appear in the denominator as well. 2. The numerator counts infant deaths during a year, and the denominator counts live births during that same year. 3. An infant who died in early 2003 may have been born in late 2002, so that death is in the numerator but not the denominator. 4. Every fraction is a ratio, so the measure remains a ratio while failing the proportion test. 5. The numerator covers all deaths under one year, so the first option misstates it, and the denominator is live births rather than a mid-year infant population. 6. Multipliers never decide whether a fraction is a proportion, so the multiplier of 1,000 is irrelevant. _Source: CDC Principles of Epidemiology in Public Health Practice (3rd ed., US federal, public domain), Lesson 3 "Measures of Risk", section Infant mortality rate_