Core concept: Proportionate mortality ratio versus cause-specific death rate
The figures cited by the council member—
18% and
24%—are
proportionate mortality ratios (PMR). A PMR answers only one question: among all people who died, what fraction died from a specific cause? It does not measure how likely a living person is to die from that cause. The actual risk of dying from cardiovascular disease is captured by the
cause-specific death rate, which uses the total midyear population as the denominator.
Calculating the cause-specific death rate for cardiovascular disease shows a slight decline. In the year before last, the rate was
72 ÷ 60,000 × 100,000 = 120.0 per 100,000. Last year, it was
72 ÷ 62,000 × 100,000 = 116.1 per 100,000. The number of cardiovascular deaths stayed exactly the same at
72, while the population grew. Therefore, the risk of dying from cardiovascular disease did not rise—it fell modestly.
The PMR rose from 18% to 24% only because deaths from other causes dropped sharply, from 328 to 228, while cardiovascular deaths remained constant at 72. When the denominator of a proportion shrinks, the proportion itself can rise even if the numerator does not change. This is a classic pitfall in interpreting mortality statistics.
Watch out! A rising PMR is often misinterpreted as evidence of increasing disease risk. The PMR is a measure of
relative cause composition among deaths, not a measure of
mortality risk in the population.
Key point! To judge whether residents faced a higher risk of dying from cardiovascular disease, use the cause-specific death rate, not the PMR. The cause-specific death rate here fell from 120.0 to 116.1 per 100,000.
The provided reference on the proportionate mortality ratio reinforces this distinction. It notes that the PMR is a ratio of deaths from a cause of interest to deaths from other causes, and that interpreting it as a direct measure of risk requires specific conditions. The abstract highlights that an alternative—the
mortality odds ratio—can be interpreted as an observed-to-expected ratio, but the PMR itself remains a measure of cause composition among decedents. In this municipality, the shift in composition reflects fewer competing deaths, not a worsening cardiovascular burden.
| Measure | Formula (last year) | Value | What it tells you |
|---|
| Proportionate mortality ratio (PMR) | Cardiovascular deaths ÷ total deaths × 100 | 72 ÷ 300 × 100 = 24% | Share of all deaths due to cardiovascular disease |
| Cause-specific death rate | Cardiovascular deaths ÷ midyear population × 100,000 | 72 ÷ 62,000 × 100,000 = 116.1 | Risk of dying from cardiovascular disease in the population |
The council member’s observation is arithmetically correct, but the conclusion drawn from it is not.
The share rose because other deaths fell, not because the risk of cardiovascular death rose. Deaths from other causes declined from
328 to
228, which mechanically increased the cardiovascular share of a smaller total. This is the best-supported conclusion from the data.