Examining the relationship between clinical monitoring and suicide risk among patients with depression: matched case-control study and instrumental variable approaches.

OBJECTIVE: To assess the relationship between closer monitoring of depressed patients during high-risk treatment periods and death from suicide, using two analytic approaches. DATA SOURCE: VA patients receiving depression treatment between 1999 and 2004. STUDY
DESIGN: First, a case-control design was used, adjusting for age, gender, and high-risk days (1,032 cases and 2,058 controls). Second, an instrumental variable (IV) approach (N=714,106) was used, with IVs of (1) average monitoring rates in the VA facility of most use and (2) monitoring rates of VA facilities weighted inversely by distance from patients' residences. PRINCIPAL
FINDINGS: The case-control approach indicated a modest increase in suicide risk with each additional visit (odds ratio=1.02; 95 percent confidence interval=1.002, 1.04). The "facility used" IV estimate indicated near zero change in risk (0.0008 percent increase; p=.97) with each additional visit, while the distance-weighted IV estimate indicated a 0.032 percent decrease in risk (p=.29). An alternative analysis assuming a threshold effect of ≥4 visits during high-risk periods also showed a decrease (0.15 percent; p=.08) using the distance IV.
CONCLUSIONS: The IV approach appeared to address the selection bias more appropriately than the case-control analysis. Neither analysis clearly indicated that closer monitoring during high-risk periods was significantly associated with reduced suicide risks, but the distance-weighted IV estimate suggested a potentially protective effect.