Assay sensitivity

Assay sensitivity is a property of a clinical trial defined as the ability to distinguish an effective treatment from a less effective or ineffective treatment. Without assay sensitivity, a trial cannot be said to make a distinction between the efficacy of two treatments.

Importance
Assay sensitivity has different implications for trials intended to show differences between treatments (superiority trials) and trials intended to show non-inferiority.

If a trial is intended to demonstrate efficacy by showing superiority of a test treatment to control lacks assay sensitivity, it will fail to show that the test treatment is superior and will fail to lead to a conclusion of efficacy.

In contrast, if a trial is intended to demonstrate efficacy by showing a test treatment to be non-inferior to an active control, but lacks assay sensitivity, the trial may find an ineffective treatment to be non-inferior and could lead to an erroneous conclusion of efficacy.

When two treatments within a trial are shown to have different efficacy (i.e., when one treatment is superior), that finding itself demonstrates that the trial had assay sensitivity. In contrast, a successful non-inferiority trial (i.e., one that has shown non-inferiority), or an unsuccessful superiority trial, generally does not contain such direct evidence of assay sensitivity.

Differences in sensitivity
A trial may have different assay sensitivity depending on the effect of the treatment tested. For example, the trial may be sensitive to an effect of 10 but not an effect of 5. Clinical trials experts will not accept the validity of a finding of "difference" or "no difference" between two treatments unless another internal control confirms that the study methods have the ability to show a difference, if one exists, over the range of interest.