Among miners, 120 deaths from tuberculosis are observed over a 10-year period. Using age-specific national mortality rates applied to the miner population, 80 deaths would have been expected. What does the Standardized Mortality Ratio indicate?

• A SMR of 67, indicating lower than expected mortality
• B SMR of 150, indicating 50% excess mortality compared with the general population ✓
• C SMR of 150, indicating miners have three times the mortality of the general population
• D SMR of 0.67, indicating a protective effect of mining on tuberculosis

Explanation

SMR equals observed deaths divided by expected deaths, multiplied by 100. Here 120 divided by 80 gives an SMR of 150, meaning mortality is 50% higher than expected after adjustment for age structure. Option C misreads 150 as a risk ratio of threefold. Option A inverts the observed and expected figures. SMR is the standard summary measure in occupational epidemiology because the workforce age distribution usually differs from the general population.

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

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