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A fresh look at proportional mortality ratios
1Department of Public Health and Epidemiology, Medical School, University of Birmingham.
Abstract:
This is a review of the use of proportional mortality ratios (PMRs). District health authorities rarely concern themselves with searching for unknown causes of disease but do need to monitor the health of a population. PMRs are a good way to do this. Textbooks of epidemiology tend to see PMRs as biased measures of risk and give them little attention. This review shows that the bias is small and of no practical importance. PMR studies can be seen as case-control studies and the major bias in these studies as analogous to Berkson's fallacy. We can then use the same techniques to reduce bias in PMR studies that are used in case-control studies. These are the use of several controls, the use of positive and negative controls, and the use of only one type of death in the denominator, rather than all causes of death. This article reviews these means of minimising bias using examples to show that careful selection of controls can overcome many of the supposed problems of PMR studies. It also shows how PMRs can control confounding in a way that SMRs cannot. PMR studies should be more widely used to monitor the health of the population.
Insights
Proportional mortality ratios (PMRs) are valuable for population health monitoring. This review demonstrates that their biases are minor and manageable, making them a practical epidemiological tool.
Area of Science:
- Epidemiology
- Public Health Surveillance
Background:
- District health authorities require effective population health monitoring tools.
- Proportional Mortality Ratios (PMRs) are often overlooked in epidemiology textbooks due to perceived bias.
- Existing literature frequently cites bias as a limitation of PMRs.
Purpose of the Study:
- To re-evaluate the utility of Proportional Mortality Ratios (PMRs) for population health monitoring.
- To address and mitigate the biases associated with PMR studies.
- To demonstrate the practical application and advantages of PMRs over other methods like Standardized Mortality Ratios (SMRs).
Main Methods:
- The study reviews PMRs as a form of case-control study.
- It analyzes bias in PMRs, drawing parallels to Berkson's fallacy.
- Methods for bias reduction include using multiple controls, positive/negative controls, and specific death categories in the denominator.
Main Results:
- The bias in PMR studies is demonstrated to be small and of negligible practical importance.
- Techniques analogous to those used in case-control studies can effectively reduce bias in PMRs.
- PMRs offer advantages in controlling confounding compared to SMRs.
Conclusions:
- PMRs are a robust and practical tool for monitoring population health.
- Careful selection of controls can overcome significant limitations in PMR studies.
- PMRs should be more widely adopted for public health surveillance.