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Do suicide barriers save lives?

Garrett Glasgow sent along this study on the effectiveness of suicide barriers on bridges:

With support from mental health workers, elected officials, the California Highway Patrol, and the local community, Caltrans has announced their intention to install a suicide prevention barrier on the Cold Spring Bridge by 2010 at a cost of $605,000. During the course of the debate a number of people have claimed that such a barrier would not only deter suicides at the Cold Spring Bridge, but actually prevent suicides and thus save lives. This claim is unfounded. A review of the evidence presented in favor of building the barrier and my own research reveals that there is no evidence that installing a suicide prevention barrier on the Cold Spring Bridge would save lives.

As Garrett writes, “there is a distinction between preventing suicides and preventing suicides
at a particular location.”

10 Comments

  1. derek says:

    A few years ago I read an article claiming that when all the ovens in Britain were converted from coal gas to natural gas (which contains no toxic CO), suicides from ovens naturally dropped to near zero, but there was no corresponding increase in suicide by other methods, implying that if an entire method becomes unavailable, total suicides do indeed decrease. (my google fu fails to find an authoritative discussion of this on the Internet, only several brief passages claiming the same thing)

    I think I've also read that the difference in suicide rates between e.g. UK and US can be largely accounted for by the difference in suicide by shooting, which in turn can be correlated to the prevalence of firearms possession in the two countries. Again, the implication is that if some favourite suicide method is not available, people often do not then commit suicide by another method, but, like Dorothy Parker, conclude that they "may as well live".

    Of course, suicide barriers on one bridge do not prevent "suicide by falling from a high place", so these factoids are not necessarily relevant.

  2. Ben Hyde says:

    There is a wide spread desire in the population to play pooh sticks as well. What we need is a study that shows that barriers to keep hooligans from dropping rocks on passing cars only displaces elsewhere.

  3. Garrett Glasgow says:

    The coal gas studies in the UK are really interesting, but it's unclear to me how much they teach us about suicide barriers on bridges.

    It could be that restricting access to lethal agents that you find in the home (poisonous gas, handguns) reduces suicides, but restricting access to methods of suicide that involve people seeking them out is ineffective.

    Another possibility is that the coal gas studies may have omitted some important confounding variables — every study on this topic that I've seen includes no control variables in the regression.

    I found this in my own simple regressions looking at the number of bridges and the suicide rate in each state. If suicide prevention barriers save lives by preventing impulsive suicides, we'd expect areas with more unsecured bridges to have a higher suicide rate, yet I found that areas with more bridges actually had lower suicide rates. I doubt this means that bridges prevent suicides. Instead, I suspect that bridges are a proxy for urban areas (which tend to have lower suicide rates) or a strong state economy.

  4. ZBicyclist says:

    Glasgow undermines his arguments by an inappropriate graph in which he compares the NUMBER of bridges (which will be affected by the size of the state) with the RATE of suicide (which controls for the size of the state's population).

    This is too long for a comment (and I want to show the graph), so I've posted this here:

    http://mikekr.blogspot.com/2007/11/bad-graph-mars

  5. Igor Carron says:

    For those bridges over land, or other touristic monuments having those safeguards, I am sure one can say that there is a decrease of deaths associated with people being with falling bodies. I am sure I have heard of one or two cases involving Notre Dame and the Eiffel tower where this occurred. I am sure it is not statically relevant though. What would be more statically relevant would be people opening up gas in their flats and taking out an entire building at the same time.

    Cheers,

    Igor.

  6. Garrett Glasgow says:

    ZBicyclist, you are absolutely correct. I presented that graph with total bridges because I thought it would be easier for people to understand, but I can see now it makes it look like I'm trying to "stack the deck."

    A revised version of the graph looking at the relationship between bridges per 100,000 and suicides per 100,000 is posted here:

    http://www.polsci.ucsb.edu/faculty/glasgow/update

    The relationship between bridges and suicides remains negative in this graph, which is not what we'd expect to see if bridges are related to impulsive suicides (and thus require suicide prevention barriers).

    Thank you for pointing this out to me.

  7. Frédér says:

    Derek, this could be the reference you are looking for:
    Kreitman, N. (1976). The coal gas story. British Journal of Preventive & Social Medicine, 30,
    86–93.

    This review could be of interest too: D. Lester. "Preventing suicide by restricting access to methods for suicide"
    (http://www.springerlink.com/content/3cldrn1pu4py3…)

    Lester seems to have written lots on the topic (indeed, his review cites 50 or so of his own papers :-)

    Disclaimer: I have not read any of these, and in particular, can not say anything about their statistical methods.

    Frédéric

  8. Thom says:

    As I understand it, action in the UK to reduce the pack size of paracetamol from 32 to 16 did correspond to a decrease in successful suicide attempts. This suggests that some interventions can reduce suicides. The interesting thing is what the important features are. Many suicide attempts are (at least partly) or impulsive and presumably just involve taking whatever is to hand or a whole pack.

    For the bridge example I reckon the precise location of the bridge might also be important. There might be a case for protecting a bridge close to an area densely inhabited by a vulnerable population (especially one with restricted capacity to travel) – for example close to a high school or university.

  9. Garrett Glasgow says:

    Thom, that's another good point that I haven't seen addressed very carefully in the literature.

    There was one case study done on a bridge in New Zealand that was across the street from a hospital with psychiatric patients, which seems to be a likely location for impulsive suicides.

    However, there are also bridges that take some effort to get to that also see suicides. For instance, the Cold Spring Bridge here in Santa Barbara County is about a 20 minute drive into the mountains from downtown. Does that make a difference? I'm not sure if anyone has ever tried to answer that question.

  10. I am a psychiatrist working in Sri Lanka involved in suicide prevention services. The next project we plan to implement is to remove Yellow Oleander trees from residential and public areas. Yellow Oleander poisoning is a leading cause of suicidal deaths in this part of the country.

    I believe that evidence available is convincing enough to embark on projects of this nature.