Comparative Effectiveness of Ruptured Cerebral Aneurysm Therapies: Propensity Score Analysis of Clipping versus Coiling

Sensitivity analysis of unmeasured confounders. Sensitivity analysis was performed by use of the lower 95% confidence interval of the odds ratio of discharge to long-term care (1.12). The x-axis represents the hypothetical prevalence of an unmeasured confounder in the clipping group; y-axis represents the hypothetical odds ratio associated with this unmeasured confounder. Curved lines represent the required strength of unmeasured confounder (defined by odds ratio[s]) that would be required to nullify the observed differences in discharge to long-term care between treated groups at selected confounder prevalence rates within the coiling group (5%, 10%, 20%, 30%, and 40%). For a given prevalence within the coiling group, a single unmeasured confounder could potentially nullify significant differences in study outcomes if the data point representing associated odds ratio and clipping prevalence is on or above the depicted curve. Point A depicts an example of a confounder with a prevalence of 15% in the clipping group and 5% in the coiling group; in this case, an odds ratio of approximately 2.2 is needed to nullify the significant difference in discharge to long-term care. If the prevalence of the same confounder increased to 10% in the coiling group, an odds ratio of approximately 4.3 (point B) would be needed to nullify the significant difference.