Dear all,
the standardized mortality ratio (SMR) is computed as the number of
observed deaths divided by the number of "expected deaths". The latter
is computed as the observed person years times the mortality rate in
some reference population.
(Actually, nominator and denominator are usually split up as sum over
age- and calendar intervals.)
What does this statistic estimate --- what is the "true SMR"?
I understand "expected deaths" as number of deaths that would have
occurred if the study population had the mortality rate of the
reference population. How is it justified then to use the observed
person years which result from the mortality of the cohort under
study rather than the mortality of the reference population?
Any hints are appreciated.
Juergen
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