December 8, 2017

Attributing risk

Some time in the next week or so, we should be getting the ACC Christmas Sermon, where we get told about how many accidents happen on Christmas Day. From last year’s version in the Herald

Every year, more than 3400 claims are lodged with ACC for Christmas Day incidents, costing the country almost $3million.

As I always point out, that’s a lot less than the number lodged on a typical day that isn’t Christmas.  On the other hand, many of those 3400 are genuinely Christmas-caused injuries; accidents that would not have happened on some random day in summer.

You can look at Christmas-attributable risk by considering individual cases and counting the number that involve new toys, Christmas trees, batteries inserted in appropriately, misuse of wrapping paper, etc, etc. Or, you can compare Christmas to an otherwise similar day.

Rafa at Simply Statistics writes about a more serious example.

The official death toll from Hurricane María in Puerto Rico is 55. That’s 55 people whose death can be specifically and clearly attributed to the hurricane. However, the number of recorded deaths from all causes in September was 2838, which is 455 above the average for September in recent years. The next largest exceedance in the past seven years was just over 200 in November 2014.

Attributing deaths on a case-by-case basis to a disaster like María is hard; it would be hard to make those sorts of decisions even without the continuing post-hurricane disruption. Another example is deaths due to the 2003 power outage in New York, where there were 6 officially-attributed deaths but a spike of 90 in the total death statistics.

Sometimes we want to look at specifically attributable cases: when snow shuts down the roads, we probably want to count the number of snow-caused crashes without subtracting the number of snow-prevented ones. But for natural disasters it’s probably the total excess deaths we want.

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Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »

Comments

  • avatar
    Steve Curtis

    They had 10 deaths in Victoria Australia from ‘thunderstorm asthma’ for one short period. That along with 8500 hospitalisations made for a major strain on medical emergency services.

    6 years ago

    • avatar
      Thomas Lumley

      Yes, that’s an example where the attribution is pretty straightforward, though it would still be worth looking to see if there was an increase in deaths that weren’t recognised as related to thunderstorm asthma.

      6 years ago