We propose a method to decompose the young adult mortality hump by cause of death. This method is based on a flexible shape decomposition of mortality rates that separates cause-of-death contributions to the hump from senescent mortality.
We apply the method to U.S. males and females 1959–562015.
Results: show divergence between time trends of hump and observed deaths, both for all-cause and cause-specific mortality. The study of the hump shape reveals age, period, and cohort effects, suggesting that it is formed by a complex combination of different forces of biological and socioeconomic nature. Male and female humps share some traits in all-cause shape and trend, but they also differ by their overall magnitude and cause-specific contributions.
Notably, among males, the contributions of traffic and other accidents were progressively replaced by those of suicides, homicides, and poisonings; among females, traffic accidents remained the major contributor to the hump.
…Figure 6 shows surfaces of raw (undecomposed) cause-of-death rates. Visually, the all-cause surface does not reveal any hump because all rates for young ages are dwarfed by the levels reached in old age as a result of the senescence component. This is also the case for non-traffic accidents, which have a strong senescence component. All other causes of death that were identified as potential contributors to the hump display relatively high mortality during early adulthood. Some causes, however, combine this with other age patterns; for example, traffic accidents present a bimodal shape, with high mortality levels during early adulthood as well as old age (not visible because of truncation of ages above 70). Suicides also strongly affect older males and middle-aged females. This picture of raw rates confirms that the causes of death that contribute to the hump often also contribute to senescence or ontogenescence. Considering all deaths from these 7 causes as relating to the young adult mortality hump would be an overgeneralization.
[Saloni discussion: The contours of death: Okay, I just enjoy giving spooky titles to my subheadings, but this chart’s very interesting.
It shows death rates in the US across two dimensions: time and age.
The shades represent death rates, and splodges show when death rates have risen. The contour lines around the splodges are like an elevation map: they show how much death rates have risen (or fallen). You can see how they’ve risen and fallen over time (on the x-axis) and across age groups (on the y-axis).
You’ll see that events with wider splodges occurred over longer time periods. Events with taller splodges affected many age groups.
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For example, look at poisonings, which includes substance use and overdoses. Here, it shows the opioid crisis, and you can see it rising gradually across adult age groups.
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Or look at the HIV/AIDS panel: as an exponentially-growing epidemic, it surged over a very short period of time, especially among young and middle-aged adults.
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Or look at traffic accidents, which were especially deadly among young people and the elderly, but have become less so over time.
Suddenly, the plots I’m used to seeing—line charts where something rises for some age groups—seem quite flat, even when they show the same data.
The shapes show how events permeate across a population and time. I think they also give visual clues about the nature of the underlying events: Were they constrained to only affecting a particular age group? Did they grow exponentially over time? And maybe these tell us something about how and why they happened.]