President Barack Obama claimed that “states with the most gun laws tend to have the fewest gun deaths.” Republican presidential candidate Carly Fiorina, meanwhile, has made nearly the opposite claim, saying states with stringent gun control laws have “the highest gun crime rates in the nation.”

In looking solely at the numbers of gun deaths and gun crimes, the data back up Obama, not Fiorina. But both politicians imply a causation that’s impossible to prove — that gun control laws lead to fewer or greater gun crimes or gun deaths.

Obama talked about gun deaths, while Fiorina said “gun crime rates,” which could include aggravated assault and robberies. Let’s start with gun deaths.

Obama’s Argument

The president made his comments on Oct. 1 after a mass shooting that day at a community college in Roseburg, Oregon, left 10 people dead, including the shooter.

Obama, Oct. 1: We know that states with the most gun laws tend to have the fewest gun deaths. So the notion that gun laws don’t work, or just will make it harder for law-abiding citizens and criminals [to] still get their guns is not borne out by the evidence.

The Centers for Disease Control and Prevention publishes statistics on firearm deaths and the death rate, which would be a fairer measure in comparing states of various populations. The death rate is the number of deaths per 100,000 people. The CDC also gives age-adjusted death rates, since such rates are influenced by the age of the population. This levels the comparison between different groups.

For 2013, the 10 states with the highest firearm age-adjusted death rates were: Alaska (19.8), Louisiana (19.3), Mississippi (17.8), Alabama (17.6), Arkansas (16.8), Wyoming (16.7), Montana (16.7), Oklahoma (16.5), New Mexico (15.5) and Tennessee (15.4).

The 10 states with the lowest firearm age-adjusted death rates were, starting with the lowest: Hawaii (2.6), Massachusetts (3.1), New York (4.2), Connecticut (4.4), Rhode Island (5.3), New Jersey (5.7), New Hampshire (6.4), Minnesota (7.6), California (7.7) and Iowa (8.0).

Firearm deaths, however, include suicides, and there are a lot of them. In 2013, there were a total of 33,636 firearm deaths, and 21,175, or 63 percent, were suicides, according to the CDC. Homicides made up 11,208, or 33 percent, of those firearm deaths. The rest were unintentional discharges (505), legal intervention/war (467) and undetermined (281).

Homicide data for 2013 don’t give us a clear picture of homicides only by firearm; however, 70 percent of homicides for the year were by firearm. The 10 states with the highest homicide rates were: Louisiana, Mississippi, Alabama, Arkansas, Maryland, Oklahoma, South Carolina, New Mexico, Missouri and Michigan. That lists includes six states that also have the highest firearm death rates.

The 10 states with the lowest homicide rates are: North Dakota, Vermont, Wyoming, New Hampshire, Utah, Idaho, Iowa, Maine, Massachusetts and Oregon.

The number of homicides that occurred in the first three states were so low that their death rates were zero. Wyoming is an interesting case, because it has one of the highest firearm death rates but a homicide rate of zero.

What role do gun control laws play in these statistics? It’s difficult to say. One news report that compiled these same CDC numbers on firearm death rates, by 24/7 Wall Street and published by USA Today, listed several reasons besides gun laws that these states might have high rates of gun deaths (suicides included). Many of the states also have higher rates of poverty, lower educational attainment and perhaps more rural areas that make getting to a hospital in time to save someone’s life difficult.

But that report also noted weaker gun laws were common among the states with higher gun death rates: “In fact, none of the states with the most gun violence require permits to purchase rifles, shotguns, or handguns. Gun owners are also not required to register their weapons in any of these states. Meanwhile, many of the states with the least gun violence require a permit or other form of identification to buy a gun,” reporter Thomas C. Frohlich wrote.

The Brady Campaign to Prevent Gun Violence and the Law Center to Prevent Gun Violence, both groups that advocate for strong gun laws, published a scorecard on state gun laws in 2013, giving higher letter grades to states with stronger gun laws. Nine of the 10 states with the highest firearm death rates, according to the CDC, got an “F” for their gun laws, and one of them got a “D-.” (Note that most states — 26 of them — received an “F.”) Seven of the states with the lowest firearm death rates got a “B” or higher; two received a “C” or “C-“; and one — New Hampshire — got a “D-.”

But again, that’s a correlation, not a causation. And the homicide rate statistics don’t show the same pattern. Eight of the 10 states with the highest homicide rates and eight of the 10 states with the lowest homicide rates all got “D” or “F” grades from the Brady Campaign analysis.

We have written before about gun control issues, and the inability to determine causation between gun laws and gun violence. As Susan B. Sorenson, a professor of social policy at the University of Pennsylvania, told us in 2012, “We really don’t have answers to a lot of the questions that we should have answers to.” And that’s partly because a scientific random study — in which one group of people had guns or permissive gun laws, and another group didn’t — isn’t possible.

When we asked the White House about Obama’s claim, a spokesman sent us links to other studies that found states with more gun restrictions had fewer gun deaths, backing up Obama’s claim that “states with the most gun laws tend to have the fewest gun deaths.” But it doesn’t back up his claim that “the evidence” shows there is a link between the gun deaths and gun laws.

Researchers at Boston Children’s Hospital and the Harvard School of Public Health looked at gun laws and gun deaths in all 50 states from 2007 to 2010, concluding that: “A higher number of firearm laws in a state are associated with a lower rate of firearm fatalities in the state, overall and for suicides and homicides individually.” Their research was published in JAMA Internal Medicine in May 2013. But the study said that it couldn’t determine cause-and-effect.

One of the authors, Dr. Eric Fleegler, a pediatric emergency medicine physician at Boston Children’s Hospital, told the Boston Globe that “[i]n states with the most laws, we found a dramatic decreased rate in firearm fatalities, though we can’t say for certain that these laws have led to fewer deaths.”

Fiorina’s Claim

Fiorina made her claim on Sept. 24 in a speech in Greenville, South Carolina, when asked about her views on guns (see the 43:40 mark). She said that the gun laws currently on the books aren’t enforced. “That is why you see in state after state after state with some of the most stringent gun control laws in the nation also having the highest gun crime rates in the nation. Chicago would be an example,” she said.

We asked the Fiorina campaign for support for that claim, and to clarify whether she meant states or cities, since she mentioned Chicago. We have not received a response, but we will update this article if we do.

Fiorina said “gun crime rates,” not just “gun deaths,” as the president claimed. The FBI has statistics on violent crimes committed with a firearm, including murder, robbery and aggravated assault, though its data come from voluntary reporting from law enforcement agencies. When we last researched firearm deaths, experts advised us to use the CDC data, since it came from required death-certificate reporting.

But what about robberies with a firearm, or aggravated assaults? We calculated firearm robbery rates for the states, using the FBI data for 2014, and the states with the highest rates are Nevada, Mississippi, Georgia, Maryland and Louisiana. Four out of five of those states received an “F” from the groups that advocate tougher gun laws. (We discounted Illinois, which reported limited data to the FBI.)

We then did the same rate calculation for aggravated assaults with a firearm in 2014. The top five states: Tennessee, South Carolina, Arkansas, Louisiana and Delaware. The last state was the only one not to receive an “F.”

As for Chicago, the Pew Research Center published a report in 2014 that found that while Chicago had seen a lot of murders in raw numbers, smaller cities had a higher rate, adjusted for population. Using FBI data — with the caveat that it is reported by local police agencies and not always consistently — the Pew Research Center determined that the top cities in 2012 for the murder rate were Flint, Michigan; Detroit; New Orleans; and Jackson, Mississippi. Chicago came in 21st.

An August 2013 CDC report looked at rates for gun homicides in the 50 most populous metropolitan areas. It found that for 2009-2010, the top gun murder rate areas were, in order: New Orleans, Memphis, Detroit, Birmingham, St. Louis, Baltimore, Jacksonville, Kansas City, Philadelphia and Chicago.

Six of those cities are in states with poor scores for their gun laws, while the other four get a “C” or better. Chicago, which placed last in the top 10, had a ban on handguns at the time. There’s no discernible pattern among those cities, nor clear or convincing evidence in these statistics that shows more gun laws lead to more or less gun crime.

— Lori Robertson