How do you compute adjusted rates with the direct method?

• A. Need overall crude rate and population size
• B. Need subgroup-specific rates for each subgroup and a standard population
• C. Need the standard population and aggregated rate across subgroups
• D. Need the number of subgroups and their frequencies

Answer: (B)

Direct standardization computes an adjusted rate by combining subgroup-specific rates with a fixed standard population. You take the observed rate for each subgroup in the study population and apply it to the number (or size) of people in that same subgroup within a chosen standard population. For each subgroup, multiply its rate by the standard population count in that subgroup to get expected cases. Sum all those expected cases across subgroups, then divide by the total size of the standard population to obtain the adjusted rate. This yields a rate that would occur if the study population had the same subgroup distribution as the standard population, allowing fair comparisons across populations with different compositions. If you only have a crude rate or an aggregated rate, you don’t have the necessary subgroup-specific rates to apply to the standard population. If you don’t have a standard population to weight by, you can’t perform the direct adjustment. If you only know the number of subgroups and their frequencies without the actual rates, you can’t compute the weighted adjusted rate.