# Publicly funded snow shovelling

In preparation for a class this week, I have done a simple little analysis to explore the economic case for publicly funded snow shovelling.   A number of studies have been done on the impacts of snow shovelling on heart attacks, and in the more general field of physical exertion and heart attacks.  Given the research, it seems reasonable to consider whether or not a public system of snow shovelling could save money.  Below I describe each step in the analysis.

1. Shovelling snow causes heart attacks

According to Auger et al., 2017, a man’s risk of myocardial infarction (MI) is 1.34 times higher the day following a major snowfall (20+ cm of snow) compared to no snowfall.  This tells relative risk; that is, the risk associated with snowfall compared to no-snowfall.  In order to assess the impact this has on public health, we need to have some measure of absolute heart attack risk–like an incidence rate.  It’s tricky to estimate the incidence rate in this case, however.  Choosing the annual incidence rate (around 0.002) is way too high, since this incidence is estimated over the whole year.  Indeed, the probability of heart attack on a day with 20 or more centimetres of snow is probably at least two orders of magnitude lower than the annual incidence rate.  Let’s assume that the baseline incidence is 0.00002–this is roughly the daily risk of MI.  This means that every day there is a 20 cm snowfall, the risk is of heart attack is 0.0000268 (0.00002 x 1.34).

2. There are 160,000 detached houses in Hamilton

How many men are exposed to the hazards of snow shovelling?  I base this estimate on the 2011 NHS, from which I pulled the number of households in Hamilton, and divided it by two.  This assumes half the time women shovel, and half the time men shovel, and that on average, every household has one man in it.  This gives us 80,000 men exposed to shovelling.  This is probably an overestimate, since some people hire snow-clearing companies, and some households just don’t bother shovelling at all.

3. The risk attributable to snowfall is…

Based on step 1, the risk of heart attack on the day following 20 cm of snowfall = 0.0000268.  The risk attributable to shovelling is the difference between the risk of heart attack among the exposed and the baseline risk: 0.0000268 – 0.00002 = 0.0000068 (or about 6.8 per million people).

To find out how many people suffer heart attacks in Hamilton due to a major snowfall event, we simply multiply the attributable risk by the exposed population:

0.0000068 x 80,000 = 0.544

These numbers suggest that once every two years, someone has a heart attack as a result of shovelling snow in Hamilton, assuming there is one 20 cm snow event per year.  One 20 cm snow event per year is probably a bit of an over-estimate, but reasonable enough based on these data.

4. How much does a heart attack cost the economy?

A complete assessment should include all costs, including health care, lost productivity, etc.  However, many of these costs are very hard to measure.  In Canada, health care costs are around \$30,000 per MI.  However, other losses could be greater, especially in the long run, and especially if we tried to price the value of a life.  Let’s say that each heart attack costs \$150,000.

5. Cost-benefit

If we multiply 0.544 x 150,000 we get the expected annual costs of heart attacks due to big snowfall events in Hamilton.  This gives us about \$75,000 a year.  Given the large number of households to shovel (160,000) and the costs of shovelling them (even a modest \$25 per household per season costs \$4,000,000 a year) there is no economic case for snow shovelling, at least when it comes to heart attacks.

When put into the context of public health impact for a small city like Hamilton, the results of Auger et al., 2017 are not particularly compelling.  Even if the relative risk estimate is correct, the actual impact on the population in this city is probably pretty small.  For the entire country, the impact is greater; I’d ballpark it at 40 heart attacks as a result of shovelling snow, and maybe 3 or so deaths a year.  Still, given that there are around 50,000 deaths a year (in Canada) as a result of heart disease, it seems that the impact of snowfall on MI is pretty small.

It’s also worth noting that snow shovelling may also have health benefits–like exercise, and sharing time with neighbours.  Since exercise improves health, and possibly saves money, this would make the economic case for publicly funded snow shovelling even weaker than what’s presented here.