The effect of child access prevention laws on adolescent suicide: a negative control approach

Recent publications on Child Access Prevention (CAP) laws suggest substantial protective effects on adolescent firearm suicide. However, these studies have also found comparable protective effect estimates on adolescent non-firearm suicide and adult firearm suicide, which may indicate residual confounding. Here we apply bias analysis techniques to assess the effects of CAP laws while accounting for potential unmeasured sources of bias using a negative control approach.

Using established bias formulas, we bias-adjust previously published point estimates and their 95% confidence intervals (CI) assuming that an arbitrary confounder biases all suicide-related effect estimates and that adolescent non-firearm suicide and adult firearm suicide are negative controls. Negative controls are outcomes or populations that prior subject matter suggests should not be meaningfully affected by the exposure and can be used to better understand and sometimes account for bias in the primary exposure-outcome relationship.

After bias adjustments, effect estimates were attenuated, with many of the confidence intervals including the null. Assuming that adolescent non-firearm suicide is a negative control outcome and taking a published point estimate as the bias parameter, the bias-adjusted effect estimate for adolescent firearm suicide decreased from an incidence rate ratio of 0.87 (95% CI: 0.78, 0.97) to 0.95 (95% CI: 0.85, 1.07). When adult firearm suicide was used as the negative control, the bias-adjusted estimate was 0.92 (95% CI: 0.82, 1.03).

Our findings suggest that CAP laws may have had a smaller public health impact on adolescent suicide than previously estimated. Given the strong evidence that reducing access to firearms can prevent suicide deaths, and that secure storage helps reduce access for many children, our findings underscore the need to continue to identify and promote effective ways to motivate adults to make household firearms inaccessible to children.