My earlier post indicated that gun laws in the US had little impact on the homicide rate, when demographic factors were taken into account. This makes sense – if I want to kill somebody, the lack of a gun will merely prompt me to choose another weapon. But what about suicide? The impulse to suicide is often brief, and easy access to a gun during a suicidal episode may increase the chance of dying.
To test this, I extended my previous dataset with data on educational attainment, data on religiosity, registered gun ownership data from the ATF, age-adjusted suicide rates from the CDC, poverty rates, unemployment rates, and other demographic data. I ran all that through a regression tree analysis, using R.
Suicide rates in the chart (click to zoom) are indicated by colour, ranging from 8 per 100,000 for New Jersey and New York (yellow) to 23.7 for Montana (black). Having a college degree seems to have a protective effect – states on the right of the chart, with more college degrees, had lower suicide rates. This may relate to the higher employability of college graduates. However, states at the top of the chart, with higher high school graduation rates, had higher suicide rates. I am not sure why this is the case.
Among the states with fewer college graduates, religion had a protective effect (this is consistent with other studies). States where 77% or more of the population said that religion was “somewhat important” or “very important” to them are indicated on the chart by triangles. For the states with fewer college graduates, the suicide rate was 13.6 per 100,000 for religious states, and 17.5 for less religious ones.
Finally, the highest-risk states (fewer college graduates and less religious) split according to gun ownership. States with more than 0.008 registered guns per capita are marked on the chart with an inner dot. Among the highest-risk states, the suicide rate increased from 13.9 per 100,000 to 18.6 when more guns were present. This group included Alaska (23.2 per 100,000), Arizona (17.5), Idaho (19.2), Maine (17), Montana (23.7), Nevada (18.6), North Dakota (17.3), Oregon (16.8), and Utah (21.4). Among the more religious states, registered gun ownership did not seem to have an effect (although, of course, registered gun ownership is a poor indicator of true gun ownership).
Thus the data does seem to suggest a link between gun ownership and suicide risk, but only when other risk factors are present (low religiosity and no college degree). This is exactly what we expected, and it means that suicidal (or potentially suicidal) people need to be kept away from guns.
Somebody pointed me at this interesting data the other day. The chart above (click to zoom) combines the “Gun Law Score Card” from the Law Center to Prevent Gun Violence in the US with homicide rate data from Wikipedia and voting results from the last US election. Do gun laws reduce the chance of being murdered?
Obviously, “Blue” states tend to have stricter gun laws than “Red” states (an average of B− vs D−). “Blue” states also have lower homicide rates than “Red” states (4.5 vs 5.9), and this is statistically significant (p = 0.012). There is a weak (R2 = 6%) correlation between gun laws and homicide rates, but this relationship is not statistically significant.
Whatever it is that makes you less likely to be murdered in some states than others, it does not primarily seem to be the gun laws. Poverty may be one of the relevant factors, however – median household income explains 22% of the variance in homicide rates, and when this is taken into account, any effects due to gun laws or election results disappear. “Red” states are, on the whole, simply poorer (and, conversely, poor states are more likely to vote Republican and have weak gun laws). Other demographic factors, such as the number of people with college degrees, also seem to have explanatory value as far as the murder rate is concerned. However, the phenomenon of murder does not seem to be understood as well as it could be.
In honour of the Cassini probe, the diagram above shows (to scale) the larger moons of Saturn (those over 100 km in diameter). The moons are shown in order of distance from Saturn, with Janus and Epimetheus being the closest. Titan comes between Rhea and Hyperion.
Janus, Epimetheus, Mimas, Rhea, and Phoebe are shown in black-and-white. Enceladus, Tethys, and Dione are shown in enhanced colour (combining infrared, visible, and ultraviolet). Titan is shown in infrared, which penetrates the atmospheric haze. Hyperion is in true colour, and Iapetus in false colour. Click on the image to zoom.
Farewell Stella Vie (car photo: Bart van Overbeeke; landscape: public domain)
The extensive solar car coverage on this blog is now over (until the next race). Back to ordinary science coverage now…
Here is a decoding table for World Solar Challenge team shirts, grouped by red / orange / yellow / green / blue / violet / multi-coloured / black / white. I found such a table useful in my coverage of the American race last year. For more detailed information about the teams, see my annotated teams list.
On October 8, teams in the World Solar Challenge begin their race from Darwin to Adelaide. Here are 10 things for travellers across Australia to look out for.
1. The Magellanic Clouds
The Magellanic Clouds are two small galaxies – at 160,000 light-years and 200,000 light-years, the nearest visible galactic neighbours of our Milky Way. They can be seen in the Southern Hemisphere, away from towns. The Australian Outback is the perfect place to observe them.
2. The Southern Cross
The Southern Cross (Crux) is a constellation appearing on the flags of many countries in the Southern Hemisphere, including Australia. It consists of four bright stars, with a fifth being visible to the naked eye in good conditions. The constellation can be located with the aid of the pointer stars Alpha Centauri and Beta Centauri. It can also be used to determine the South Celestial Pole. The star at the “top” of the Cross (Gamma Crucis) is a red giant. The fifth star (Epsilon Crucis) is an orange giant.
3. The wedge-tailed eagle
The wedge-tailed eagle (Aquila audax)) is Australia’s largest bird of prey, and a national icon. It can be seen around Australia, either in the sky, or snacking on roadkill.
4. The red kangaroo
The red kangaroo (Macropus rufus) is the largest living marsupial, and is found throughout central Australia, in areas with less than 500 mm rainfall. It is an Australian national icon, as well as being a major traffic hazard at dawn and dusk.
5. The sand goanna
The sand goanna (Varanus gouldii) is a large monitor lizard, growing to about 1.5 metres. It is found across much of Australia.
6. The thorny devil
The thorny devil (Moloch horridus) is found in arid, sandy areas of western and central Australia. It lives mostly on ants.
7. Magnetic termites
Magnetic termites (Amitermes meridionalis) are one of two Australian termite species building mounds that align north–south. They can be found in the vicinity of Darwin. The mound orientation appears to be a temperature-control mechanism.
8. Sturt’s desert pea
Sturt’s desert pea (Swainsona formosa) grows in arid regions of Australia. It is the floral emblem of the state of South Australia.
9. The desert grasstree
The desert grasstree (Xanthorrhoea thorntonii) is a grasstree found in arid regions of western and central Australia. Like the other 27 species of grasstree (Xanthorrhoea spp.), it is endemic to Australia, and a symbol of the Australian landscape.