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Why were the event rates so low such that the sample size had to be increased and what are the implications for generalisability of these results?

April 26, 2017event generalisability implications increased low rates results sample size

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Why were the event rates so low such that the sample size had to be increased and what are the implications for generalisability of these results?

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A. The Steering Committee took the decision to increase the sample size and tighten the inclusion criteria (all pts must have ECG evidence of ischemia and/or already elevated cardiac enzymes or markers (troponin) to at least 2x the upper limit of normal at inclusion) when the overall event rate at ~2,000 pts randomized was lower than expected. As we later learned, some of this was due to the treatment effect in the clopidogrel arm but the steering committee could not have known this at the time. As per the study protocol, the sample size calculations were based on overall event rates and were adjusted to project 1250-1500 events.