Rates and counts

From the Stuff story you could be forgiven for thinking heart disease in women is getting worse

Women have overtaken men in dying from heart disease, and the situation is forecast to get worse…

Ministry of Health figures show 5038 women died of cardiovascular disease in 2009, compared with 4712 men, and are projected to increase as the effects of diabetes and obesity worsen.

 Both those statements are true, but the implication is false.  The only thing you can reasonably talk about in health terms (as opposed to economics) is age-specific death rates.  That is, we want to correct for two trends that are not really ‘health’ changes.  The first is population size.  There are more people in New Zealand now than in the past, so there will be more deaths.  The second is age: your chance and my chance of dying of cardiovascular disease next year is higher than it was last year because we’re a year older.  We want to look at rates (fractions) rather than counts, and compare people of the same age.

Age-specific death rates from heart disease are still falling in New Zealand, as they are essentially everywhere in the Western world, and have been for my entire lifetime. That is, a 70-year old woman is less likely to die of heart disease this year than a 70-year old woman was to die of heart disease in, say, 2001, or 1980.

The improvements have been driven by a range of factors including reductions in smoking, introduction of treatments for high blood pressure and high cholesterol, and better heart-attack care. The  fall has been faster in men, who are now catching up to women.   The fall is showing signs of levelling off now for both men and women, and there are reasonable concerns that the trend might reverse in the not-too-distant future.

Since heart disease is a major cause of death for women, and this isn’t as widely appreciated by the public, an increase in targeted health promotion would probably be a good thing.  But that doesn’t mean we should regret the falls in heart disease deaths among men: a better phrasing would be “Men have caught up to women in dying of heart disease, but the situation, for both sexes, is forecast to stop improving.”