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As an American, as a Texan, as a person of mixed race with an Hispanic family, and as a scientist, I turned my anger and sadness from these weekend’s mass shootings into an opportunity to take a closer look into the public health epidemic of #GunViolence in the United States.
A diverse melting pot of people and ideas, our country sets the stage for a natural experiment across state lines in which we can use the variation across states to actually test ideas and hypotheses, including the effects of guns and gun laws on gun violence.
Common assertions are that guns do not cause violence, people do; the way to stop bad people with guns is good people with guns; and strict gun laws are ineffective at stopping gun violence because people will find a way to get them.
Evidence that would be needed to support these claims are that gun violence (A) increases with an increasing population size, (B) decreases with an increase in gun presence, and (C) decreases with more gun laws and regulations.
Because there is no centralized place where you can find these data, I used skills from my scientific training to compile a comprehensive data set using multiple sources (referenced within, cited below) for all 50 states & DC in a single year (2017). Each data point is a state.
So what do the data show?
There is some evidence for (A). In looking at the 2017 estimated population (1), an increase in population significantly correlates with firearm mortalities (2) & mass shootings (3). Because I’m a scientist and love data, I made figures so you could see these trends yourself:
These data seem to suggest that an increase in population does lead to an increase in gun violence (A). However, an increase in population also significantly correlates with an increase in the number of registered guns per state, making that association difficult to disentangle.
But in running stats for these data, the number of firearm mortalities appears to be more strongly correlated with the number of registered guns, whereas the number of mass shootings is more strongly correlated with population size.
So to conclude, there is some evidence for (A). What about (B)?

As you can see from the figures below, the more registered guns there are (4), there are significantly more firearm mortalities (2), firearm offenders (5), and #MassShootings (3).
I found these same outcomes when looking instead at the number of licensees (4), which are the primary source of guns (6) and therefore strongly correlate with the number of registered weapons within each state, as seen in this figure:
Together these data do *not* support (B) and instead show the opposite: having more guns and access to guns is linked to more gun violence and harm to people through either death or injury.
Last, in looking at two separate metrics for gun law stringency by state using two different data sources, one from 2017 data (7) and the other from 2010 data (8), I was able to assess the impact of gun regulations on gun incidents. Results from both data sets were similar.
First, I found that more gun laws (7) are associated with significantly *fewer* firearm mortalities (2).
Moreover, more gun laws (7) are associated with significantly *fewer* firearm offenders (5).
Surprisingly, I found that more gun laws (7) are associated with a *slight increase* in mass shootings (3), but this pattern was not observed when looking at the other metric for key gun law measures (8).
Together these results do *not* support (C) & instead suggest that states with more gun laws do a better job curtailing firearm incidences within them than states with lax gun laws. #GunControlWorks
Further evidence for the effectiveness of #guncontrol at the state level comes from a study that conducted a state-level assessment of gun ownership and violence.
The study identified three state laws that are most strongly associated with reduced overall firearm mortality - universal background checks, ammunition background checks, and ID requirements for firearms (9).
But lending support for the idea within (C) that “where there’s a will, there’s a way," another study used crime gun tracing data to build a theoretical model to better understand cross-state gun trafficking. It found that guns flow from states with weak regulations to nearby...
...states with strict regulations & that high possession rates by criminals are linked to weak regulations in nearby states (6).

These findings, in combination with my own analysis, suggest that weak laws at the state level are enabling loopholes that make all of us LESS safe.
To conclude, there is some evidence for (A) but not (B) or (C). State-level differences in the U.S. reveal that more #GunViolence is associated with larger populations, more firearms, and fewer & less strict gun laws and regulations
Gun violence is a public safety & national security issue that affects us all. These data support the idea that fewer guns and more strict laws make us all safer. If states are unwilling to enact such laws, then we need federal policies that will.

Your neighborhood scientist, who not only recognizes the importance of gun violence research to enact evidence-based policy to eliminate the senseless violence plaguing our families but also sees those 39,773 people killed in 2017 by firearms (10) as real people.
Here are my sources:
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