deregulation of gun carrying over the last four decades has undermined public safety—which is to say that restricting concealed carry is one gun regulation that appears to be effective." A 2016 study in the European Economic Review which examined the conflicting claims in the existing literature concluded that the evidence CCW either increases or decreases crime on average "seems weak"; the study's model found "some support to the law having a negative (but with a positive trend) effect on property crimes, and a small but positive (and increasing) effect on violent crimes". The Washington Post fact-checker concluded that it could not state that CCW laws reduced crime, as the evidence was murky and in dispute. In a 2017 article in the journal Science, Stanford University law professor John Donohue and Duke University economist Philip J. Cook write that "there is an emerging consensus that, on balance, the causal effect of deregulating concealed carry (by replacing a restrictive law with an RTC law) has been to increase violent crime". Donohue and Cook argue that the crack epidemic made it difficult to determine the causal effects of CCW laws and that this made earlier results inconclusive; recent research does not suffer the same challenges with causality. A 2018 RAND review of the literature concluded that concealed carry either has no impact on crime or that it may increase violent crime. The review said, "We found no qualifying studies showing that concealed-carry laws decreased [violent crime]." A 2020 study in PNAS found that right-to-carry laws were associated with higher firearm deaths. A 2019 panel study published in the Journal of General Internal Medicine by medical researchers including Michael Siegel of the Boston University School of Public Health and David Hemenway of the Harvard T.H. Chan School of Public Health found that “shall issue" concealed carry laws were associated with a 9% increase in homicides. A 2019 study in the American Journal of Public Health found that greater restrictions on concealed carry laws were associated with decreases in workplace homicide rates. Another 2019 study in the American Journal of Public Health found that states with right-to-carry laws were associated with a 29% higher rate of firearm workplace homicides. A 2019 study in the Journal of Empirical Legal Studies found that right-to-carry laws led to an increase in overall violent crime. A 2017 study in the American Journal of Public Health found that "shall-issue laws"