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Biometrics. 1989 Sep;45(3):1017-20.

Changing frequency of interim analysis in sequential monitoring.

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Biostatistics Research Branch, National Heart, Lung, and Blood Institute, Bethesda, Maryland 20892.


In clinical trial data monitoring, one can either introduce a discrete sequential boundary for a set of specified decision times or adopt a use function and then derive the boundary when data are monitored. If the use function approach is employed, one can adjust the frequency of data monitoring as long as the decision is not data-dependent. However, if the frequency of future data monitoring is affected by the observed data, then the probability of Type I error will no longer be preserved exactly. But the effect on the significance level and power is very small, perhaps negligible, as indicated by simulation results.

[Indexed for MEDLINE]

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