Summary of disadvantages of stopping trials early

The advantages of stopping a trial early are reasonably obvious and have been discussed above. The disadvantages of stopping a trial early are set out in Box 9.10.

With all such considerations, it should be emphasized that the decision to stop a trial at an interim analysis before its pre-planned time should not be guided only by statistical considerations, but also a variety of practical and clinical considerations. For this reason, any statistical 'rules' for early termination are usually termed guidelines.

Example. Dillman and colleagues performed a trial of chemotherapy and radiotherapy against radiotherapy alone in patients with non-small cell lung cancer [40]. The authors do not give a hazard ratio, but reading from the Kaplan-Meier survival curves report that two and three year survival was 'doubled' by the use of chemotherapy. In a letter criticizing the stopping of this trial early Souhami and colleagues [41] make the following points: the reported estimate is likely to be an overestimate; no confidence intervals are presented and thus the reader is left with no idea of the likely size of the difference; finally, only 155 of the 180 patients have been analysed. Souhami and colleagues conclude: 'In

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