The following information may be relevant to questions 12 -15. Yet another study appearing in the New England Journal of Medicine' reports the results of a randomized clinical trial conducted in China, designed to compare the efficacy of two treatments for hypertension in older adults. With regards to study design, the researchers report: "In this multicenter, randomized, controlled trial, we assigned Chinese patients 60 to 80 years of age with hypertension to a systolic blood-pressure target of 110 to less than 130 mm Hg (intensive treatment) or a target of 130 to less than 150 mm Hg (standard treatment). The primary outcome was a composite of stroke, acute coronary syndrome (acute myocardial infarction and hospitalization for unstable angina), acute decompensated heart failure, coronary revascularization, atrial fibrillation cardiovascular causes." "Of the 9624 patients screened for eligibility, 8511 were enrolled in the trial; 4243 were randomly assigned to the intensive-treatment group and 4268 to the standard-treatment group" Enrolled patients were followed for up to one year after randomization. The follow-up Kaplan-Meier was included to show the primary findings from the study:13. Which of the following statements best characterizes the proportional hazards assumption with regards to the above Cox regression model? a. The 95% confidence interval for the (true) hazard ratio does not include 1. b. The risk (hazard) of the primary outcome in the both randomization groups must be constant across the entire follow-up period. - 10 - c. The hazard ratio of the primary outcome for the "Intensive Treatment" group compared to the "Standard Treatment" group should be constant across the entire study follow-up period. d. The proportional hazard assumption is violated because the estimated Kaplan- Meier curves for the "Intensive Treatment" and "Standard Treatment" groups are not parallel1.0- 0.10- 0.8- 0.08- 0.06- 0.6- Standard treatment Cumulative Incidence 0.04- 0.4- Intensive treatment 0.02 - 0.2- 0.00- 12 18 24 30 36 42 48 0.0+ 12 18 24 30 36 42 Months since Randomization No. at Risk Standard treatment 1268 4147 4070 4000 3938 3849 3664 1200 Intensive treatment 4243 4174 $109 4039 3970 3867 3694 1234 Figure 3. Cumulative Incidence for the Primary Outcome. The Cox proportional hazard model used to quantify this association is as follows: In(hazard of primary outcome at time t) = In (1.(t) ) + -0.30x, Where x1= 1 for "Intensive Treatment" and 0 for "Standard Treatment"