subordinates the study of versions of treatment or versions of control. In particular, the main treatment-control comparison is unaffected by the exploration of versions of treatment — the usual confidence interval for a constant effect is reported — despite controlling the family-wise error rate in multiple comparisons that explore the possibility of versions of treatment with different effects. Two confidence intervals are reported, the usual interval for a constant effect and an interval designed to contain both effects if the two versions differ. If the effect is constant, then both intervals simultaneously cover that one effect with probability ≥ 1 − α , but if there are two versions then the second interval covers both version effects with probability ≥ 1 − α . The investigator always reports both intervals, valid under different assumptions. This is an unusual type of simultaneous inference: there is essentially one question, but there are two sets of assumptions underlying the answer, so one question is answered twice, as opposed to answering several different questions. There are multiple assumptions rather than multiple hypotheses. The two intervals together permit an investigator to report the conventional confidence interval for a constant effect, without lengthening it for multiple testing, yet the investigator also provides some information about whether the study’s conclusions depend on the absence of versions of treatment. The two intervals may possibly disagree, say about whether no effect is plausible, and if they do disagree then they demonstrate that the assumption about versions of treatment is playing an important role in the interpretation of the available data. Importantly, the method does not presume there is a single version of treatment by virtue of failing to reject the null hypothesis that the two versions are equal. That is, it entertains the possibility that there are versions of treatment even when the convetional interval assuming a constant treatment effect is not empty. 4