A 2013 study found that in the United States, "A higher number of firearm laws in a state are associated with a lower rate of firearm fatalities in the state."[41] A 2016 study published in The Lancet found that of 25 laws studied, and in the time period examined (2008–2010), nine were associated with reduced firearm mortality (including both homicide and suicide), nine were associated with increased mortality, and seven had an inconclusive association. The three laws most strongly associated with reduced firearm mortality were laws requiring universal background checks, background checks for ammunition sales, and identification for guns.[42] In an accompanying commentary, David Hemenway noted that this study had multiple limitations, such as not controlling for all factors that may influence gun-related deaths aside from gun control laws, and the use of 29 explanatory variables in the analysis.[43]