Since 1989, a number of states have passed laws that make gun owners criminally liable if someone is injured because a child gains unsupervised access to a gun. These laws are controversial and their effect on fire-arm injuries is unknown.
University of Washington researchers report that among 12 states who had these laws in effect for at least one year during 1990-1994, unintentional shooting deaths were reduced by 23% (95% confidence interval 6% - 37%). The authors conclude that "state safe storage laws intended to make firearms less accessible to children appear to prevent unintentional shooting deaths among children less than 15 years."
So does this study provide justification for these laws?
Not yet.
This was an ecologic epidemiology study, meaning the conclusion is based on very "macro" comparisons of groups of people. The study involved no data about individuals, just groups. Traditionally, these studies are only useful for forming hypotheses for further testing, not irrefutable facts.
In particular, no data was collected on compliance with these laws and the relationship of compliance to the decrease in injuries. There may have been fewer unintentional firearm-related injuries in states with safe storage laws, but this study assumed compliance with the laws and assumed that compliance is responsible for the decrease in injuries. A big assumption considering the result.
The reported 23% decrease in injuries is a pretty weak result--probably beyond the capability of the ecologic type of study to reliably detect. Even in the better types of epidemiology studies (i.e., cohort and case-control), rate increases of less than 100% (and rate decreases of less than 50 %) are very suspect.
So how much stock can be put in a weak result based on inadequate data?
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