# HLTH 501 – A study is conducted to estimate survival in patients following kidney transplant.; Week 8 Problems

Question HLTH 501 Week 8 Problems 15 points each. Place answers within the Word document below. 1. A study is conducted to estimate survival in patients following kidney transplant. Key factors that adversely affect success of the transplant include advanced age and diabetes. This study involves 25 participants who are 65 years of age and older and all have diabetes. Following transplant each participant is followed for up to 10 years. The following are times to death in years or the time to last contact (at which time the participant was known to be alive). Deaths: 1.2 2.5 4.3 5.6 6.7 7.3 and 8.1 years Alive: 3.4 4.1 4.2 5.7 5.9 6.3 6.4 6.5 7.3 8.2 8.6 8.9 9.4 9.5 10 10 10 and 10 years Use the life table approach to estimate the survival function. Use years intervals of 0?2; 2?4; Complete the table below. Interval in Years Number At Risk During Interval Nt Average Number At Risk During Interval Nt* =Nt-Ct /2 Number of Deaths During Interval Dt Lost to Follow-Up Ct Proportion Dying qt = Dt/Nt* Proportion Surviving pt = 1-qt Survival Probability St= pt*St-1 0?2 2?4 4?6 6?8 8?10 Use the Kaplan-Meier approach to estimate the survival function. Complete the table below Time Years Number at Risk Nt Number of Deaths Dt Number Censored Ct Survival Probability St+1= St*((Nt-Dt)/Nt) 0 25 1.2 2.5 3.4 4.1 4.2 4.3 5.6 5.7 5.9 6.3 6.4 6.5 6.7 7.3 8.1 8.2 8.6 8.9 9.4 9.5 10.0 Referring to the graph above: What is the probability of surviving 6.5 years? A. None B. 0.85 C. 0.60 D. 0.90 Patients have an 85% chance of surviving how many years? A. 6.0 B. 4.25 C. 3.2 D. 5.5 2. A clinical trial is conducted to evaluate the efficacy of a new drug for prevention of hypertension in patients with pre-hypertension (defined as systolic blood pressure between 120?139 mmHg or diastolic blood pressure between 80?89 mmHg). A total of 20 patients are randomized to receive the new drug or a currently available drug for treatment of high blood pressure. Participants are followed for up to 12 months and time to progression to hypertension is measured. The experiences of participants in each arm of the trial are shown below. New Drug Currently Available Drug Hypertension Free of Hypertension Hypertension Free of Hypertension 7 8 6 8 8 8 7 9 10 8 9 11 9 10 11 11 11 12 12 12 Estimate the survival (time to progression to hypertension) functions for each treatment group using the Kaplan-Meier approach. New Drug Complete the table below. Time Months Number at Risk Nt Number of Events (Hypertension) Dt Number Censored Ct Survival Probability St+1= St*((Nt-Dt)/Nt) 0 10 7 8 9 10 11 12 Currently Available Drug Complete the table below. Time Weeks Number at Risk Nt Number of Events (Hypertension) Dt Number Censored Ct Survival Probability St+1= St*((Nt-Dt)/Nt) 0 10 6 7 8 9 10 11 12 To answer the question as to whether or not there is a difference in time to progression a Chi square statistic is computed. The critical value for rejection of the null hypothesis is 3.84. The computed Chi square is 0.335. Based on comparing the computed Chi square and the critical Chi square which of the following is (are) true? A. There is not statistically significant evidence to show that thetime to progression is different between groups. B. There is statistically significant evidence to show that thetime to progression is different between groups. C. The time to progression is essentially the same for each group. D. a and c. The hazard ratio risk of progression to hypertension is 0.658. Based on this computation which of the following is (are) true? A. The risk of progression to hypertension is reduced by 34.2% in patients assigned to the new drug as compared to the currently available drug. B. The risk of progression to hypertension is 1.52 times higher in patient?s current drug as compared to the new drug. C. The risk of progression to hypertension is 5.12 times higher in patient?s current drug as compared to the new drug D. a and b

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