Practical considerations for approximating relative risk by the standardized mortality ratio.

The standardized mortality ratio is a widely used and often criticized summary statistic for studies of occupational mortality. In this paper the authors discuss practical conditions under which relative risk can reasonably be approximated by the standardized mortality ratio. When the true relative risk is greater than 100%, the standardized mortality ratio overestimates relative risk no matter how small the mortality rates or how short the age bands utilized in the analysis. However, when the excessive mortality is consistent across the age bands, the standardized mortality ratio can usefully approximate relative risk for some applications, such as those involving site-specific cancers, providing the age bands employed are not too large.