A clinical trial was conducted to test the efficacy of different vitamin supplements (namely, Vitamin E) in preventing visual loss in patients with retinitis pigmentosa (RP). Visual loss was measured by loss of retinal function as characterized by a 50% decline in the electroretinogram (ERG) 30 Hz amplitude, a measure of the electrical activity in the retina. In normal people, the normal range for ERG 30 Hz amplitude is (microvolts). In patients with RP, ERG 30 Hz amplitude is usually and is often . Approximately 50% of patients with ERG 30 Hz amplitudes near are legally blind compared with <10% of patients whose ERG 30 Hz amplitudes are near (the average ERG amplitude for patients in this clinical trial). Patients in the study were randomized to one of two treatment groups. The first group received high-dose (400 IU) vitamin E supplements. The second group received low-dose (3 IU - trace amount) Vitamin E supplements. Patients were enrolled in 1984-1987, and follow-up was terminated in September 1991. Because follow-up was terminated at the same point in chronological time, the period of follow-up differed for each patient. Patients who entered early in the study were followed for 6 years, whereas patients who enrolled later in the study were followed for 4 years. In addition, some patients dropped out of the study before September 1991 and had not failed. Dropouts were due to death, other disease, side effects possibly due to the study medications, or unwillingness to comply (take study medications). In the following table, we present data from the RP clinical trial described above concerning the effect of high-dose vitamin E (400 IU/day) vs. low-dose vitamin E (3 IU/day) on survival (where failure is loss of at least 50% of initial ERG 30 Hz amplitude). Note that survival in the context of this problem is a patient losing less than 50% of initial ERG 30 Hz amplitude. 400 IU of vitamin E daily Fail Censored Survive Total 0-1 year 7 3 170 180 1-2 year 9 2 159 170 2-3 year 22 2 135 159 3-4 year 24 27 84 135 4-5 year 13 32 39 84 5-6 year 11 28 0 39 3 IU of vitamin E daily Fail Censored Survive Total 0-1 year 4 1 169 174 1-2 year 10 3 156 169 2-3 year 14 1 141 156 3-4 year 16 27 98 141 4-5 year 15 34 49 98 5-6 year 7 42 0 49 Problem 1 Estimate the hazard function by year for each group. Problem 2 Estimate the survival probability by year for each group.

Question

A clinical trial was conducted to test the efficacy of different vitamin supplements (namely, Vitamin E) in preventing visual loss in patients with retinitis pigmentosa (RP).

Visual loss was measured by loss of retinal function as characterized by a 50% decline in the electroretinogram (ERG) 30 Hz amplitude, a measure of the electrical activity in the retina. In normal people, the normal range for ERG 30 Hz amplitude is (microvolts). In patients with RP, ERG 30 Hz amplitude is usually and is often . Approximately 50% of patients with ERG 30 Hz amplitudes near are legally blind compared with <10% of patients whose ERG 30 Hz amplitudes are near (the average ERG amplitude for patients in this clinical trial).

Patients in the study were randomized to one of two treatment groups. The first group received high-dose (400 IU) vitamin E supplements. The second group received low-dose (3 IU - trace amount) Vitamin E supplements.

Patients were enrolled in 1984-1987, and follow-up was terminated in September 1991. Because follow-up was terminated at the same point in chronological time, the period of follow-up differed for each patient. Patients who entered early in the study were followed for 6 years, whereas patients who enrolled later in the study were followed for 4 years. In addition, some patients dropped out of the study before September 1991 and had not failed. Dropouts were due to death, other disease, side effects possibly due to the study medications, or unwillingness to comply (take study medications).

In the following table, we present data from the RP clinical trial described above concerning the effect of high-dose vitamin E (400 IU/day) vs. low-dose vitamin E (3 IU/day) on survival (where failure is loss of at least 50% of initial ERG 30 Hz amplitude). Note that survival in the context of this problem is a patient losing less than 50% of initial ERG 30 Hz amplitude.