Kathy, In this situation I dont think there is an "alpha" penalty for this -- there is no "penalty for looking at data" there is a penalty when the interim analysis can result in a stop, claim, or "victory" it is actions or possible actions, that cause penalties... there is nothing in it that "looking" at data causes a penalty of some sort. Now, concerns could be raised on what was done at this interim... would they have claimed significance if it were reached?? Can you present a p-value in the paper and say "significant"... this becomes a possible issue -- but not insurmountable. You need to report that the primary time hasn't been reached and the primary of the second trial not yet conducted. This is in part why typically researchers are hypersensitive about just not looking.
What a concern here can be is "operational bias" -- that by disclosing some data -- by investigators, patients, etc, seeing information about outcomes affects behavior of the clinicians and subjects (maybe that drop from the study, maybe seek other treatments... ) It is likely more worry than actual problem -- and given you are 4 years in a 5 year study hard to imagine it could impact things... but be prepared to defend this issue. The kind of endpoint, the type of treatment, etc could make this a non-issue, or a possible issue.
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Scott Berry
Berry Consultants
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