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Fig. 4 | BMC Medical Research Methodology

Fig. 4

From: Time dependent hazard ratio estimation using instrumental variables without conditioning on an omitted covariate

Fig. 4

Kaplan-Meier estimates for the survival curves (top). Dashed vertical line stands for the perioperative period (30 days) while numbers indicate the patients at risk each 2 years within the CAS and CEA groups). At botton, histograms for the instrumental variable distributions (left) and box-plot (right) for both the CEA and the CAS groups. Notice that a value of zero in the IV implies that in the hospital this patient received the surgery, no CEA surgeries were performed in the 12 months prior to that patient. On the other hand, a value of 1 implies that, in this hospital, in the last 12 months, all patients received CEA

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