In the United States, access to firearms is associated with an increased risk of completed suicide.[59] A 1992 case-control study in the New England Journal of Medicine showed an association between estimated household firearm ownership and suicide rates, finding that individuals living in a home where firearms are present are more likely to commit suicide than those individuals who do not own firearms, by a factor of 3 or 4.[1][60] A 2006 study by researchers from the Harvard School of Public Health found a significant association between changes in estimated household gun ownership rates and suicide rates in the United States among men, women, and children.[61] A 2007 study by the same research team found that in the United States, estimated household gun ownership rates were strongly associated with overall suicide rates and gun suicide rates, but not with non-gun suicide rates.[62] A 2013 study reproduced this finding, even after controlling for different underlying rates of suicidal behavior by states.[63] A 2015 study also found a strong association between estimated gun ownership rates in American cities and rates of both overall and gun suicide, but not with non-gun suicide.[64] Correlation studies comparing different countries do not always find a statistically significant effect.[65]:30 A 2016 cross-sectional study showed a strong association between estimated household gun ownership rates and gun-related suicide rates among men and women in the United States. The same study found a strong association between estimated gun ownership rates and overall suicide rates, but only in men.[66] During the 1980s and early 1990s, there was a strong upward trend in adolescent suicides with guns[67] as well as a sharp overall increase in suicides among those age 75 and over.[68]