A few days to cool off and think things through may be enough to prevent hundreds of homicides each year, according to a new study in PNAS.

A study tracking handgun laws on wait periods over a 45-year period found that a delay in obtaining a firearm after purchase reduced gun homicides by 17 percent. That breaks down to about 36 homicides per year for the average state. As of 2014, such laws in 16 states and the District of Columbia prevented about 750 gun homicides per year. If all 50 states required a wait, around 910 more lives could be spared, the authors report.

“Waiting periods would therefore reduce gun violence without imposing any restrictions on who can own a gun,” according to the authors, led by Deepak Malhotra, a negotiation and conflict-resolution expert at Harvard Business School.

About 33,000 people die in America from gun violence each year, mostly from suicides. The researchers found waiting periods reduce suicides as well, but the association wasn’t as strong and varied in different analyses from a 6 to 11 percent reduction. That would work out to a range of about 17 to 35 fewer suicides each year for an average state.

There have been hints in the research before that wait periods can reduce gun deaths, specifically suicides. For instance, a 2000 study in JAMA by violence researchers Jens Ludwig and Philip Cook found that waiting periods imposed by the Brady Handgun Violence Prevention Act between 1994 and 1998 reduced suicides among people aged 55 years and older. But the study saw no significant change in homicides from the switch. And the question of wait periods’ effect on gun homicides has lingered, leaving many policy makers to think that they are ineffective.

Malhotra and his colleagues argue that this is not the case. They note that the 2000 JAMA study found no effect because the study mis-coded 16 states. Those states were identified as being impacted by the Brady Act even though they previously had wait-period laws on the books. “As a result,” the authors conclude, “the coding of Brady states in the study by Ludwig and Cook fails to capture all states that had preexisting waiting periods,” Malhotra and co-authors concluded.

Cook and Ludwig did not immediately respond to Ars’ request for comment.

Delayed data

For the new study, Malhotra and colleagues repeated the analysis of the Brady Act’s impact and also looked at a wider timeframe: from 1970 to 2014. In that 45-year span, 43 states and DC had waiting period laws on the books for at least one year, which typically call for a delay of two to seven days.

To assess the impact of the laws, the researchers looked at the “difference-in-differences.” Basically, they compared the changes in gun deaths in states with new laws with any changes seen in states without new laws. The researchers controlled for economic and demographic differences between states, such as poverty levels, race and age breakdowns, and alcohol consumption trends.

In the 45-year analysis, they found that waiting periods slashed homicides by 17 percent and suicides by seven to 11 percent. That would work out to about 36 fewer homicides and 22 to 35 fewer suicides per year in an average state.

Next, the researchers narrowed their focus to just 1990 to 1998, when the federal Brady Act forced many states to adopt new waiting periods and background checks. They again saw a 17 percent dip in homicides from wait periods as well as a six percent drop in suicides. That works out to about 39 fewer homicides and 17 fewer suicides for an average state during that time frame.

The study doesn’t provide any clues as to how waiting periods might stifle deaths. But the researchers speculate that any delay may “close the window of opportunity” for any would-be criminals and “deter purchases among people who have malevolent, but temporary, motivations.” For the suicidal, the delay may allow them to rethink their plans

Data on non-gun-related deaths suggests that homicidal people subject to waiting periods don’t substitute other weapons as means to commit suicide. However, there’s some evidence to suggest that some suicidal people may find another method if they can’t readily acquire a gun.

Malhotra and his colleagues note that waiting periods have broad support from the medical community as well as most Americans—including gun-owning Americans.

Last week, a collection of top medical experts wrote yet another commentary labeling the burden of firearm-related deaths and injuries in the US as a “health care crisis.” They called doctors and healthcare professionals to action to try to identify, develop, and implement policies and practices that could reduce harms—just as they would if they were reacting to an infectious disease outbreak.

“As health care professionals, we don’t throw up our hands in defeat because a disease seems to be incurable. We work to incrementally and continuously reduce its burden. That’s our job.”

The commentary was signed by Darren B. Taichman, executive deputy editor of Annals of Internal Medicine; Christine Laine, editor-in-chief of Annals of Internal Medicine; Howard Bauchner, editor-in-chief of JAMA and the JAMA Network; Jeffrey Drazen, editor-in-chief of New England Journal of Medicine; and Larry Peiperl, chief editor of PLOS Medicine.

PNAS, 2017. DOI: 10.1073/pnas.1619896114 (About DOIs).