Comparisons of survival time estimates for niigata prefecture (japan) residents exposed to ingested arsenic

Survival analysis was used to analyze follow‐up data on an arsenic‐poisoned area, identified in 1959, in order to assess the effect of arsenic on survival time. The subjects were 443 residents of Namiki‐cho, Nakajo‐machi, Niigata Prefecture, Japan, who ingested well water contaminated with arsenic between 1955 and 1959. Their exposure to arsenic was only by ingestion of well water. We observed this historical cohort from October 1959 to February 1992. Survival time was calculated in two ways: from 1959 (the end of exposure) until death or until 1992 (the termination of follow‐up); or from birth until death or until 1992. The entire cohort was divided into two groups according to the arsenic concentration measured in the wells in 1959. Different survival curves of the two were drawn using the Kaplan–Meier method. The lifetime survival curves indicate that the lifetimes of arsenic‐exposed residents were significantly shorter than that of the low‐dose exposure group or of unexposed residents. From the differences in the estimated lifetime survival curves, the effect of arsenic on the mortality of the residents can be inferred.