Lawmakers have been caught up in another debate over gun laws in the wake of the school shooting in Parkland, Florida.
But a new study published Friday shows how limited research on guns makes it difficult to determine which policies can help curb the problem.
The RAND Corporation, a nonpartisan think tank, released its results from a review of thousands of studies on gun control policies and found only 62 that established a direct causal relationship between policies and outcomes such as reduced homicide and suicide rates.
RAND found that the most comprehensive studies on gun policies were conducted by the National Research Council in 2004 and by Robert Hahn and colleagues in 2005.
Overall, RAND researchers said the base of research was too thin to draw any conclusions about which gun policies are the most effective at curbing gun violence.
Researchers attributed the lack of research to a lack of federal funding for research. Congress attached the so-called Dickey Amendment -- a provision lobbied by the National Rifle Association -- to the omnibus spending bill.
The Amendment prohibits the Centers for Disease Control and Prevention from spending federal dollars on research on gun control policies.
RAND spent two years and nearly $1 million on the project, which also included a survey of gun policy experts and the establishment of a research database on state gun laws.
The gun policy experts RAND interviewed disagreed widely on which policies did and didn't reduce violence, but they did agree that reducing suicide and homicides should be the main objectives of any gun policies.
RAND identified 13 types of gun policies and reviewed them against 8 types of outcomes. Due to a lack of studies, most of the results were weak or inconclusive.
However, there was strong evidence to suggest reducing children's access to guns reduces the number of suicides and unintentional deaths and injuries.
RAND found moderate evidence to suggest background checks reduce suicides and violent crime, but the impact on mass shootings was inconclusive.
Researchers found moderate evidence suggesting stand-your-ground laws may lead to more homicides.