Stand Your Ground Laws

Stand Your Ground laws and Castle Doctrine laws exist in 22 States.  Stand Your Ground laws implement a legal framework that allows the use of deadly force without a duty to retreat if a person reasonably fears for his or her life or safety.  Castle Doctrine laws allow the use of deadly force if your home is invaded;  these laws assume that home invasion implicitly threatens bodily harm or death to the home's occupants. Supporters cite that these laws make their residents safer or at least make the residents safer that avail themselves of firearm protection.  

Recently I became aware of a study done by two Texas A&M economists (See Link) suggesting the opposite.  That is, they suggested that incorporation of Castle Doctrine laws actually increased the number of homicides in the states in question.  I reviewed the paper and had to concede that much of their published work seemed to support their conclusions although the uptick in homicide rates did not seem too significant. After that, and with an open mind, I reviewed the data from the FBI UCR (Uniform Crime Reporting) database myself.

My conclusion is that the authors of the paper were wrong, while homicides increased slightly in the first year following implementation, overall, the homicide rate declined after that.  Also, since correlation does not imply causality, Castle Doctrine and Stand Your Ground can neither be shown to neither decrease nor increase the homicide rates 2-3 years after implementation.

Without doing all of the statistical testing that the authors did, I had to conclude that on average the homicide rate in the states that implemented Castle Doctrine and Stand Your Ground laws did in fact see an increase in homicide rates for a year or two after the laws' introduction.  After that, the homicide rates, on average, declined as did the homicide rates nationwide.  Whether I do the analysis or the Texas A&M folks do the analysis, there is simply no way to show causality either way.  Correlation does not prove causality.

Here is some data.  Note that of the 22 states involved, 16 of them implemented Stand-Your-Ground and Castle in 2005 or 2006.  4 states added the law in 2007 and two states added the law in 2008 or 2009.  Looking at all Castle law states, the data looks like:

 Okay, that's a lot of data.  Let's just look at the average data:

Here you can see an uptick in data from 2006 to 2007.  Since 16 of the 22 states added the Castle Law in 2006, we can say that homicide rates in Castle Law states did inclease, slightly, after the law was implemented.  Note that the Castle Law states have a higher homicide rate than the national average but that was true before implementation of the law.  Also, the overall average homicide rate in these states is pulled higher because of Louisiana which has homicide rates more than double the national average as you can see in the first plot.  Below is a plot with the average of Castle states neglecting Louisiana:

Here you can see that the Castle Law States are not significantly above the National average except for 2011 and 2012.  Certainly we can conclude that the Castle law states remain more dangerous than the rest of the country and non-Castle law states as a whole.

What can we say generally:  In most cases, the homicide rate went slightly higher the year after Castle Doctrine laws were implemented.  After the first year, the homicide rates decreased as did the national average.  In fact, castle law states decreased more the second year following implementation, on average, than did the non-Castle law states.  We have to conclude that, on average, Castle Law states are more dangerous than non-Castle law states before and after implementation of Castle Doctrine laws.  There may be differences in enforcement density (number of police per unit area) or cultural differences that account for this.

Overall, the data does not show that Castle laws are detrimental to public health.