John Spens

The Newtown massacre drew immediate public demand for new gun control and bans on assault rifles.  In response to this outcry, many gun rights advocates sought to change the conversation, focusing on underlying causes of violence rather than the guns themselves.  In some cases, these advocates put forward intelligent and factual arguments.  In others, however, efforts to down play relationships between guns and violence involved highly misleading information.  For example, here is an info-graph that has emerged on the Internet.  This same message is the subject of this Fox News article.

The data presented here seems to indicate that hammers cause more deaths than assault weapons.  One might also extrapolate from this piece that gun-related violence is a relatively small issue, on scale with other types of violence, such as bludgeoning or stabbing.

The actual source of this data is not provided, but these numbers do correspond with data provided to me by my colleague, Dr. Ken Collier.  Ken pointed me to a table on the U.S. Department of Justice / Bureau of Justice Statistics website.  This table contains homicide aggregates for 2011, categorized by motive and method.  Assuming that the individual who created this graphic was using this table, the numbers presented correspond to the total number of people murdered in 2011 by rifles and the total number of people murdered in 2011 by blunt instruments (which includes hammers).  What is important to note is what has been overlooked in this graphic.  The number of homicides committed by rifles is only a small part of the picture.

Those 323 homicides represent only four percent of all firearm-related homicides in 2011.  If we take all firearm-related homicides into account, we derive a very different set of ratios between firearm-related deaths and “death by hammer”:

• Of the 12,664 recorded homicides that occurred in 2011, 68% of those were caused by firearms.  More than two out of every three homicides was committed using a firearm.  This is a ratio that has remained relatively constant for the past 30 years.
• In comparison, only 13% of homicides involved a sharp instrument; knives, scissors, box cutter, etc.  Homicide victims in 2011 were five times more likely to be shot to death than stabbed to death.
• Only 4% of homicides in 2011 involved blunt instruments such as hammers, clubs, etc. Homicide victims in 2011 were seventeen times more likely to be shot to death than bludgeoned to death.

There is potential validity to the argument that assault rifles represent a tiny fraction of homicides committed in the U.S., given that a large percentage of homicides (72%) are perpetrated with handguns.  However, the important point that we must continue to recognize, and that the author of the Fox News article fails to note, is that gun-related violence is a major issue in this country and the relationship between firearms and violent crime must be explored and addressed.

In my last posting I had demonstrated that “Right to Carry” legislation had no verifiable impact on the homicide rate in those states that had adopted it.  A number of people who read that posting asked if I would perform a similar analysis regarding the impact of gun control legislation.  If enabling citizens to bear arms in public had no demonstrable impact on violence, would removing their ability to bear arms have any impact?  And if gun control did have an impact, would it be positive or negative?Two cities in the US (Chicago and Washington DC) have enacted legislation that specifically bans the ownership of handguns.  In both cases, those laws were eventually found unconstitutional and overturned.   I will first focus on Washington DC.  In 1975, The Firearms Control Regulations Act was established.  This law prohibited residents from owning handguns, automatic weapons and high-capacity semi-automatic weapons.  Those citizens who had purchased and registerted handguns prior to 1976 were allowed to keep them but were not allowed to carry them in public.  This law was challenged on the basis that it violated citizens’ second amendment rights and was overturned in 2008.The goal of this analysis is to determine if any conclusions can be drawn from the roughly thirty years that this law was in effect.  I will explore two scenarios:

• Did preventing citizens from bearing handguns reduce the levels violence in Washington DC?
• Conversely, did removing criminals’ concerns about citizens being able to defend themselves actually lead to an increase in violence?

As in my last analysis, I have selected the overall homicide rate (homicides per 100,000 people) as the figure of merit.  While assessing the specific impact on firearm-related homicides and violence would be enable us to draw more specific conclusions, the intent of these laws is to have an overall impact on violence.  If gun control legislation only impacts the method by which people killed, then such legislation is ultimately ineffective.The statistics for homicides in Washington DC have been extracted from the US Justice Department’s Uniform Crime Reporting Statistics site.  The following graph depicts the homicide rate for the District of Columbia from 1965 – 2010.

It is immediately evident that Washington DC experienced a massive spike in homicides during this 30-year period.  Based on this data, it would be impossible to make any claims that the introduction of the Firearms Control Regulations Act had a positive impact on violence.   The question is, does this data indicate that the removal of a citizen’s right to bear arms lead to an uptick in violence?I would argue it does not.  While there is clearly a dramatic jump in homicide rates from 1986 to 1991, that trend begins to reverse itself in 1992 and is essentially negated by 2005.   If we compare the homicide rate for the year prior to the law going into effect (1975) and the first full year after the law was overturned (2008), there was a net decrease in homicide rates of 4%.  Since a simple year over year comparison can be misleading, I calculated the mean homicide rate for the years 1960 to 1976 and the mean homicide rate for 2008 to 2010. The mean homicide rate for the years preceding the gun ban was 24.3.  The average homicide rate for the years following the law’s repeal was 25.9.  This represents a 6.57% increase.If we take the set of the homicide rates for the years preceding and following the ban, we see that the mean homicide rate was 24.7, with a coefficient of variance of 36%.  Given the small population size and the degree of variance, a 7% fluctuation cannot be considered statistically relevant and it is impossible to derive any conclusions from the change in homicide rates.

Because the trend was corrected well before the reinstatement of 2^nd amendment rights, there is no real correlation between the ability to bear arms in public and the increase in crime.  What did cause this bump?  The jump experienced during this period has been attributed to illegal drug use, particularly the “crack epidemic” of the 1980’s through 1990’s.   Increases in major crime rates (not only homicides) during this period were particularly prevalent in areas of higher poverty, such as Washington DC.  I have started to validate this hypothesis by correlating homicides and drug-related crime, but obtaining a quantitative measure of the extent of drug crime is proving challenging.Even without establishing this relationship, I think it is safe to say that Washington DC’s efforts to band handguns had no demonstrable impact on the homicide rate in that city.   This seems reasonable, as the law did little to eliminate the existing supply of handguns from the criminal population, or even reduce the number of legal gun owners as of 1976.  Furthermore, gun control legislation at the municipal level does virtually nothing to prevent individuals from procuring guns in nearby areas without gun control legislation.  Until gun control legislation is ubiquitous and includes measures to reduce the number of illegal guns in circulation, it will probably be very challenging to demonstrate whether such legislation is effective.At the same time, this data refutes the argument that an armed public is required to deter crime. While the crime rate significantly increased shortly after the ban went in place, an equally significant reduction was also achieved while the ban was in place.  If armed citizens are critical to deterring crime, then rates should have continued to increase until the law was repealed.

“The only thing that stops a bad guy with a gun is a good guy with a gun”

Wayne LaPierre, EVP, NRA

A point made by many gun rights proponents is that firearms are essential for self-defense.  Many have argued that removing firearms from the public would result in higher crime rates, as criminals would be less concerned about potentially lethal consequences.  To demonstrate this, gun rights advocates will point to the introduction of “right to carry” legislation; laws that defend the rights of gun owners to carry and conceal weapons on their person in public.  Supporters of right to carry legislation will point to crime statistics from states that have either banned concealed weapons or to crime statistics from those states that have instituted right to carry legislation to support this argument.After reading one such claim, I started researching these statistics online.  The first site I was directed to was justfacts.com.  Justfacts.com is a site that provides data and some analyses on a range of social topics.  While the mission statement of the site is to present unbiased reporting of facts, the authors of the site openly admit to conservative perspectives.  The authors indicate that they intentionally do not provide analyses or assessments of their findings so as to not persuade readers in a specific direction.  They prefer that the facts speak for themselves.There are three graphs on the JustFacts site that I selected for analysis.  These graphs depict the homicide rates (homicides per 100,000 people) of three states: Michigan, Florida and Texas.  I have pulled the following images from their site:Note that in all three cases, the authors pointed out that each state’s homicide rate was, on average, some percentage lower after the right to carry law was put in effect.  Furthermore, that reduction was greater than the average drop experienced in the US overall.  These statements would seem to imply that the introduction of right to carry laws has had a positive impact on the homicide rate in three states.  Note that the authors do not explicitly make a conclusion, they only point out this difference in each case.I decided to test if there is any validity to such a conclusion.  Was the reduction in homicide rates experienced in these states statistically meaningful? Could a causal relationship be implied (not necessarily proven, just implied) from the changes that occurred after the right to carry laws went into effect?Before continuing I must point out that justfacts.com is using overall homicide rates and not specifically firearm-related homicides.  Optimally justfacts.com would only employ firearm-related homicide rates for this analysis.  Changes in the rate of other methods of homicide such as blunt force trauma could skew the overall homicide rate.  However, I have observed that the ratio of firearm-related homicides to total homicides in the US has remained consistently at 65% over the past 30 years, only deviating significantly due to the events of 2001. Given this, and that my goal is to assess the validity of the findings given the data employed by justfacts.com, I continued using total homicide statistics.Looking at the three graphs, I immediately noticed the following:

1. All three states appear to have experienced higher homicide rates than the overall US homicide rates until the early to middle part of the 1990’s
2. By 2000, these three states were much more closely aligned to the US homicide rate

My objective was to measure this change in relation to the dates that Right to Carry laws were enacted in each state.I started by seeking to duplicate the work done by justfacts.com and producing the graphs depicting the individual state homicide rate per 100,000 residents against the US homicide rate over the past 50 years.  The justfact.com authors thoroughly site their data sources.  In this case, the data was provided by the US Justice Department’s Uniform Crime Reporting Statistics site.  Using this site I was able to extract violent crime statistics for each state from 1960 to 2010.  I generated this comparison for each state and committed graphs with these comparisons to the Sandy Hook project repository.Having produced the same results as justfacts.com, I then sought to compare the trends experienced in Florida, Michigan and Texas to the remaining US states.  From the US homicide rate, I could see that there had been a peak in homicide rates in the early 1990’s followed by a steady decline to 2010.  I wanted to understand how consistent this pattern was across states.  This would allow me to assess if the rates experienced in these three states were anomalous or not.

This graph depicts the overall US rate (a weighted average), the mean homicide rate for the set of states (an un-weighted average) and the standard deviation from that mean for each year.I then calculated the difference between the homicide rates experienced each of the three states and the mean over the fifty year period.  This would provide the following information:

• How the fluctuations in the homicide rate deviate from the rest of the country.  The difference from the mean should identify the occurrence of trends that are potentially significant.
• Whether the differences displayed are statistically significant.  I have included the standard deviation to provide a frame of reference.  Over the course of the fifty years plotted, one standard deviation contains between 54% and 70% of the states in a given year.  Two standard deviations contain between 94% and 100% of the states in a given year.  This provides a good reference for what is statistically relevant behavior and what is a natural variation.

I started with Texas.  This first graph is similar to the graph published on justfacts.com  This graph demonstrates that until 1996, the homicide rate in Texas was substantially higher than the national average.  This is the same year that Texas enacted the right to carry law.

However, when we look at how Texas differs from the mean homicide rate, we get a different picture:

We can see that the real downward trend preceded the implementation of the right to carry law.  Once the law was in effect, the homicide rate for Texas remained relatively consistent with the mean homicide rate.  It even trends very slightly higher.  The point made by justfacts.com that the “…Texas murder rate has averaged 30% lower than it was before the law took effect, while the U.S. murder rate has averaged 28% lower” is due to the fact that the homicide rate in Texas was considerably higher to begin with.  During the period of 1976 through 1991, Texas was in the top 10% of homicide rates in the nation.  There is no statistical evidence that indicates the right to carry law has had a measurable impact on homicide rates in Texas.The findings for Florida were similar.

Florida experienced a general downward trend starting in 1980, seven years prior to the introduction of the law, but still remains above the mean homicide rate and consistent with the national average homicide rate.

Michigan enacted the right to carry law in 2001.  That was five years after the homicide rate experienced a consistent eight-year downward trend.  Since the enactment of law, there have been some isolated dips but the homicide rate has remained statistically consistent.

Based on this analysis, I see no evidence indicating that the right to carry law has had a material impact on these three states.  As of 2010, these states all remain at or above the national average and above the mean homicide rate among the fifty states.  While their respective homicide rates have improved, in every case these improvements preceded the introduction of the right to carry law.  While the data provided by JustFacts.org is  accurate and the statistics they have generated are correct, their analysis is lacking and fails to paint a full picture.  Their statements could easily be misconstrued by those who do not thoroughly investigate the data behind the statistics.The data for this analysis can be found here.

My first analysis for the Sandy Hook Project involved comparing US homicide rates, and firearm-related homicide rates, with those of other countries.  There were two questions I wanted to explore:

1. How do the level of gun-related deaths in the US compare to countries of similar levels of prosperity?
2. Which countries experience similar levels of gun-related deaths as the US?

While these numbers have been presented numerous times in the past, I wanted to ensure that I fully understood the data sources and methodologies employed for calculating the homicide rates.I started with the mortality statistics published each year in the National Vital Statistics Report of Deaths published by the Center for Disease Control (CDC).   These reports provide a detailed breakdown of US deaths by method and intent.  Using these reports, I was able to compile 30 years of data regarding firearm-related deaths.

There were two interesting findings derived from this effort.  First, the homicide rate in the US has reduced by 50% over the past 20 years.  While recent events might create the impression that gun-related violence is on the rise, overall firearm violence continues to trend lower.  Second, a close relationship has existed between homicide rates and firearm-related deaths over the past 30 years.  While I haven’t demonstrated the relationship mathematically, visually the relationship is striking.  The only significant deviation appears to be due to the events of 9/11/2001.  This does not prove a causal relationship between firearms and homicides but it definitely indicates that further exploration of this relationship is warranted.I then compared these homicide rates with those of other countries.  For the comparison to be relevant, I sought out countries with similar levels of prosperity to the US.  Using the World Bank figures for gross domestic product per capita (or Purchasing Power Parity) I identified a set of sixteen countries with a PPP between 125% and 70% of the USA.  I excluded countries such as Luxembourg, Qatar and Brunei, as their relatively small populations might make comparisons irrelevant.I obtained mortality data for over 100 countries from the World Health Organization’s Statistical Information System (WHOSIS).  To get the cause and intent, I had to employ the raw data provided by the WHO.  Unfortunately, details regarding the method and intent were only effectively captured in the tenth revision of the International Classification of Diseases (ICD-10).  Therefore, only the date ranges of 1999 to 2010 are useful.   Furthermore, data is not complete for all countries for this date range.   For this reason, I selected data collected in 2006 to compare countries.

Once again, the findings were striking.  Homicide rates in the US were more than three times that of Finland, the second highest on the list. The rate of firearm-related homicides in the US was greater than 8 times that of Canada, the second highest rate of firearm-related homicides amongst this grouping of countries.In a second pass, I sought to identify countries with similar homicide rates as the US.  I ordered the reporting countries by homicide rate for 2006 and selected eight countries preceding and seven countries succeeding the US in that list.

Of these countries, five stand out particularly for the same relatively high proportion of firearm-related homicides: Mexico, Costa Rica, Nicaragua, Thailand and Argentina.In subsequent postings I will explore the attributes of these five countries to understand what characteristics they share in common.  An aspiration of mine would be to produce a model that accurately represents these relationships, but given the small set of countries I am working with I am not confident in the viability of that.For me, this first effort provides a strong indication that even though gun related homicides in the US have been consistently trending lower,  the level of violence, and particularly firearm-related violence is out of proportion with the prosperity and maturity of our society.The data for this analysis can be found here.