Microkhan by Brendan I. Koerner

The Bridge Factor

December 14th, 2009 · 5 Comments

Suicide and Bridges
In the course of questioning the utility of suicide-proof barriers on bridges, a political scientist makes an intriguing observation:

In order to determine if exposure to bridges increases the suicide rate, I examined the relationship between the suicide rate and the number of bridges likely to attract suicidal individuals in all 50 states plus Washington D.C. from 1979 through 2004 (the only years for which complete data was available). Bridges likely to attract suicide victims were defined as those bridges over 30 meters (about 98 feet) high with pedestrian access. In order to statistically test the relationship between the number of bridges and the suicide rate in a state in a given year, I use a technique known as linear regression. Essentially, this is the process of fitting a trend line to a scatter plot of data, and then testing to see if the trend line has a positive, zero, or negative slope. If increased exposure to bridges leads to more suicides, we would expect to see more suicides in states that have more bridges, and thus a positively sloping trend line.

This figure reveals that there is a negative relationship between the overall suicide rate and the number of bridges in a state, exactly the opposite of the relationship we would expect to see if bridges helped cause suicides and suicide prevention barriers saved lives. It does not seem plausible that increasing the number of bridges in a state would directly reduce the suicide rate – instead, the number of bridges in a state may be a proxy for some other factor that reduces the suicide rate (such as a robust state economy). At any rate, there is no evidence to suggest that increased exposure to bridges increases the suicide rate.

The author then makes a leap to contend that this means barriers have little effect, since people intent on suicide will simply find another way of bringing about their own demise. While we’re not entirely sold on that line of argument, we have previously made clear that decades worth of anti-suicide measures seem to have done little to affect America’s overall suicide rate. So clearly whatever we’re doing now isn’t working as well as we’d hope.

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