Deltoid

Alan Watt said:

However, what effect did WW-I have on the age-distribution of the population? I would expect the percentage of 18-25 year-olds in the general population to be reduced due to war casualties. In the U.S., this is the age group which accounts for most of the violent crime.

Here are the percentages of the population of NSW that were between 18 and 25 inclusive at each census year:

      Male   Female
1911   8.4%     8.2%
1921   6.4%     7.1%
1933   7.3%     7.0%

This suggests that the male percentage would have been 7.4 in 1921 were it not for the Great War. However, I suspect that this overestimates the effects of the war - see below.

Also, I don't know how Australian military forces are organized, but in G.B., they are (or were at the time) grouped in units by geographical area. That is, each regiment would be composed of people from the same place. A unit which got wiped out therefore consisted of a lot of neighbors and relatives. If the war casualties did have a significant effect on the age distribution of the population most likely to commit violent crime, it would also tend to have a very high regional variation, or at least higher than the same casualty rates would have on the U.S., which deliberately homogenizes its forces.

I don't think losses were proportionately more in NSW than elsewhere.

I also don't know the Australian casualties in WW-I;

60,000 dead, or 1.2% of the entire population. This suggests that the calculation above, which suggests that 1% of the population, or 80% of the deaths occured in the age group 18-25 in 1921, which was the age group 11-18 at the start of the war and 15-22 at the end, overstates the effect of the war on the 18-25 group.

In any case, this could explain part of the decline that followed gun control, but not all, since the percentage decline in the homicide rate was greater than the percentage decline in the fraction of the population male 18-25. Furthermore, while males 18-25 are the most likely to murder, they are responsible for only 25% of the homicides in NSW. (This was measured over the period 1968-1981, so may perhaps have changed.)

Do you think it would be interesting to recalculate the homicide rates, using not the actual population, but the population weighted by age groups, with the weights being the fraction of homicides committed by that age group. This should correct for demographic change.