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Case I: Life testing is discontinued after a fixed number, r, of items have failed. Items on test may or not be replaced. The number of items initially on test is n. The best estimate of the mean life, 0, is given by Orin = Trn/r, (2) where T,,, is the accumulated life on test until the r'th failure occurs. The observed failure times are x ,,n < x 2, < *. < Xr,n < * . For simplicity of notation, we will suppress the subscript n. If testing is terminated after r(< n) failures have occurred then, in the nonreplacement case:
Benjamin Epstein (Fri,) studied this question.