Correlation between homicide and suicide rates

I used some WHO and World Bank data to tabulate suicide and homicide rates for countries around the world.  I did this because I was wondering if the legal, social and other structural factors that influence homicide also influence suicide.  Some factors –like poverty and social inequality–may jointly contribute to more homicide and more suicide.  Other factors–like education–may contribute to less homicide and less suicide.  Yet other factors (like the age structure of the population) may result in more homicide and less suicide, or the opposite.  Looking at the correlation between the rates might indicate if and where such processes exist.

Method

This is a simple ecological correlation study at the international level.  I do not mean to imply a causal association between homicide and suicide, but that a correlation between these measures could suggest the existence of some common factors that influences both.  A large number of countries are missing from this analysis because of incomplete data, or because the data linkage would have required some manual tinkering with country names, but I came up with data for 94 countries for analysis.  Here is the R code, here are the homicide and suicide data, and here are the population data.

Results

There is a moderate correlation (R=0.35) between the log of suicide and the log of homicide rates.  More interesting is the graphical representation of this relationship:

intentional_injuries_international

There are three visible clusters here.  First is the high homicide-high suicide group, which are mostly countries in Central and South America (orange circle).  Then there is the lower homicide and higher suicide group (blue circle), which is wealthier European countries.  The remaining cluster (green circle) is more dispersed, but seems to show a more clearly proportional relationship between suicide and homicide.

Conclusions

What’s the take away message here?  Homicide and suicide are both the result of human decisions, but there is a clear structural process at work.  This process is very likely complex and multidimensional, but suggests that legal, cultural, social and economic forces influence these decisions at a fundamental level.  Wealthier western countries seem to have more structural controls over homicide, and fewer controls over suicide. Less homicide could be due to the prohibition of guns or efficacy of law enforcement, neither of which would be as effective at preventing suicide.  Central American countries have less structural controls over homicide, but more structural controls over suicide–the former is probably the result of the social dysfunction associated with the drug trade, and the latter could be influenced by religion.  For the remaining countries of the world the relationship seems more complex, but does suggest that the structural controls over homicide and suicide might be similar.

Limitations

Some of these data are not entirely trustworthy.  The homicide rate in Honduras is too low in these data, possibly due to under-reporting in health data; I defined homicide from the WHO database that uses ICD10 codes.  Honduras may not have a good vital statistics system that codes homicide properly.   Or there could be a mistake somewhere.  In spite of this, overall, the data look reasonable.  In the future, it would be interesting to see how this pattern emerges over time.