  While the gold standard for clinical trials is to blind all parties --
participants, researchers, and evaluators -- to treatment assignment, this is
not always a possibility. When some or all of the above individuals know the
treatment assignment, this leaves the study open to the introduction of
post-randomization biases. In the Strategies to Reduce Injuries and Develop
Confidence in Elders (STRIDE) trial, we were presented with the potential for
the unblinded clinicians administering the treatment, as well as the
individuals enrolled in the study, to introduce ascertainment bias into some
but not all events comprising the primary outcome. In this manuscript, we
present ways to estimate the ascertainment bias for a time-to-event outcome,
and discuss its impact on the overall power of a trial versus changing of the
outcome definition to a more stringent unbiased definition that restricts
attention to measurements less subject to potentially differential assessment.
We found that for the majority of situations, it is better to revise the
definition to a more stringent definition, as was done in STRIDE, even though
fewer events may be observed.
