The following represents survival data for a hypothetical cohort study comparing two exposures. The observed times X represent years since entry into the cohort. The censoring indicator tells whether the subject dies ( = 1) or was still alive ( = 0) at last observation.

Exposure A: X: 3 6 9 14 23

: 1 1 1 0 1

Exposure B: X: 6 7 17 19 26

: 1 0 1 1 0

Calculate, by hand, the Kaplan-Meier (i.e., product-limit) estimator of the survival curve () for each of the two exposure groups. Compute, by hand, the estimated variance of () at each uncensored observation for the two exposure groups.

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