Assessing maturity and reliability of data

The Kaplan-Meier survival curves for the BA06 bladder cancer trial [3] are shown in Fig. 9.4. The report gives the median follow-up of patients still alive at four years. We can see from this figure that the curves, and therefore their comparison, are still reliable at five years (an important timepoint in this disease), since the total numbers at risk in the chemotherapy and no chemotherapy groups at five years are ninety-three and eighty, respectively. In the design, the plan was to reliably detect (approximately 90 per cent power, 5 per cent significance level) a difference at two years from 50 per cent survival in the no chemotherapy group to 60 per cent survival in the chemotherapy group, and to recruit 915 patients, and observing 460 deaths. The trial was actually reported when 485 deaths have been observed. Finally, 53 per cent (485/915) of patients have died. All these observations taken together show that this trial was reported as planned and is appropriately mature.

Time from randomization (months)

Patients at risk

No chemotherapy 485 355 257 187 132 80

Chemotherapy 491 372 283 200 139 93

Fig. 9.4 Overall survival, BA06 bladder cancer trial. Reprinted with permission from Elsevier Science (The Lancet, 1999, 354, 533-40).

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