SMR is the ratio of the number of deaths observed in the study group to the number of deaths in the study population (if the study population had the same age specific rates as the standard population) multipied by 100.
This allows coparison of death rates across different groups
SMR = (observed number of deaths / expected number of deaths) x 100
An SMR of 125 is 25% more than expected
An SMR of 100 is the study has the same number of deaths as expected
An SMR of 75 means there 25% less deaths than expected.
OBSERVED / EXPECTED (O/E – Ollie is taller than evie – Ollie over Evie!)