(1) Rates per residents per year
§(assuming a population of 1 million residents)
§# of DDDs per year per 1000 residents for ampicillin
§ = 750,000 DDDs per year / 1,000,000 residents * 1000
= 750 DDDs per 1000 residents per year
§This could be interpreted as an estimate of how many days of treatment every resident, if placed on the drug, would have consumed in a year.