1. A clinical trial was conducted to test the efficacy of different vitamin supplements in preventing visual loss in patients with retinitis pigmentosa. Visual loss was measured by loss of retinal function as characterized by a 50% decline in the ERT (electroretinogram) 30 Hz amplitude, a measure of the electrical activity in the retina. Patients were randomized to 15,000 IU of vitamin A or 75 IU of vitamin A. Patients were enrolled in 1984-87 and follow- up was terminated in September 1991. Failure was defined as visual loss. "Censored was defined as dropouts due to death, other disease, side effects possibly due to the study medications, or unwillingness to comply. D Ct 172 t 0 1 2 3 4 5 6 15,000 IU of vitamin A Rt 0 0 3 4 172 6 0 165 15 1 159 21 26 143 15 35 96 5 41 46 t 0 1 2 3 4 5 6 75 IU of vitamin A D Ct 0 0 8 0 13 3 21 2 28 13 31 13 29 Rt 182 182 174 158 135 86 42 21 mno t = time in years De = number of deaths during year t Ct = number of censored during year t Rt = number surviving to beginning of interval t (a) Create life tables for each treatment group that contain the probability of dying and surviving in each interval, and the cumulative probability of survival. 1. A clinical trial was conducted to test the efficacy of different vitamin supplements in preventing visual loss in patients with retinitis pigmentosa. Visual loss was measured by loss of retinal function as characterized by a 50% decline in the ERT (electroretinogram) 30 Hz amplitude, a measure of the electrical activity in the retina. Patients were randomized to 15,000 IU of vitamin A or 75 IU of vitamin A. Patients were enrolled in 1984-87 and follow- up was terminated in September 1991. Failure was defined as visual loss. "Censored was defined as dropouts due to death, other disease, side effects possibly due to the study medications, or unwillingness to comply. D Ct 172 t 0 1 2 3 4 5 6 15,000 IU of vitamin A Rt 0 0 3 4 172 6 0 165 15 1 159 21 26 143 15 35 96 5 41 46 t 0 1 2 3 4 5 6 75 IU of vitamin A D Ct 0 0 8 0 13 3 21 2 28 13 31 13 29 Rt 182 182 174 158 135 86 42 21 mno t = time in years De = number of deaths during year t Ct = number of censored during year t Rt = number surviving to beginning of interval t (a) Create life tables for each treatment group that contain the probability of dying and surviving in each interval, and the cumulative probability of survival