Clinical Epidemiology & Evidence-Based Medicine Terminology
Specific to Epidemiology July 02, 2005 Outcome and Factor
Measures: - Proportion: A dimensionless number between 0.0 an
1.0 (if a probability) or, equivalently, between 0% and 100% (if
a percentage) consisting of one count as the numerator divided
by another count as the denominator. Note that for consistent,
unbiased interpretation, 1) all the individuals in the numerator
must also be included in the denominator, 2) each individual in
the denominator must be at risk of being in the numerator, and
3) all the individuals at risk of being in the numerator in a
group must be in the denominator. Equivalently, the probability
that an at-risk individual will acquire a condition. Point
prevalence is a proportion. Proportions are often miss-
identified as "rates" (e.g. case-fatality "rate", attack "rate",
pregnancy "rate", relapse "rate"). (Note: Some introductory
texts mislabel these proportions as "rates".) - Rate: An
instantaneous or "velocity" measure tha