In vital statistics, the 'Standardized Mortality Ratio' (SMR) is calculated to compare mortality between populations with different age structures. An SMR of 1.30 for an occupational group of coal miners indicates:

• A Coal miners have a 30% higher mortality than would be expected if they had the same age-specific death rates as the standard population ✓
• B Coal miners have 30% lower mortality than expected based on the standard population
• C The crude death rate in coal miners is 1.30 per 1,000
• D 30% of deaths in coal miners are directly attributable to coal dust exposure

Explanation

The Standardized Mortality Ratio (SMR) = Observed deaths / Expected deaths × 100 (or expressed as a ratio). An SMR of 1.30 (or 130 if multiplied by 100) means observed deaths are 30% higher than expected — that is, coal miners have 30% excess mortality compared to the reference population after controlling for age differences. SMR >1.0 indicates excess mortality; SMR <1.0 indicates deficit mortality (the 'healthy worker effect' where employed populations tend to be healthier than the general population). SMR is used in indirect standardization, where the standard population's age-specific rates are applied to the study population's age structure.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.