After a non-inferiority clinical trial, a new therapy may be accepted as effective, even if its treatment effect is slightly smaller than the current standard. It is therefore possible that, after a series of trials where the new therapy is slightly worse than the preceding drugs, an ineffective or harmful therapy might be incorrectly declared efficacious; this is known as “bio-creep.” Several factors may influence the rate at which bio-creep occurs, including the distribution of the effects of the new agents being tested and how that changes over time, the choice of active comparator, the method used to model the variability of the estimate of the effect of the active comparator, and changes in the effect of the active comparator from one trial to the next (violations of the constancy assumption). We performed a simulation study to examine which of these factors might lead to bio-creep and found that bio-creep was rare, except when the constancy assumption was violated.



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