Epidemiological terms are top of mind now, due to the pandemic. Here are two that often confuse: incidence and prevalence.
For example, I encountered the following sentence on a popular medical web site:
“Knee meniscal injuries are common with an incidence of 61 cases per 100,000 persons and a prevalence of 12% to 14%.”
I was confused. What was the difference between incidence and prevalence? It turns out the incidence figure needed a time period, without which the statistic was meaningless.