Table 1

Concepts and assessment criteria for responder definitions

Responder criterionFor a continuous response variable (e.g., C-peptide), the threshold demarcating clinically favorable values (e.g., preservation)
Intrasubject variabilitySometimes referred to as “biologic variability,” this term refers to the phenomenon that repeating an assay on material taken from the same subject but at different times can lead to different assay values
BiasThe amount by which a responder definition will, on average, over- or underestimate the responder percentage in a patient population
False responder rateThe percentage of subjects that are classified as responders by the responder definition but who actually are nonresponders
False nonresponder rateThe percentage of subjects that are classified as nonresponders by the responder definition but who actually are responders
ReliabilityRefers to the false responder and false nonresponder rates collectively
External validityIn general, concordance with the findings of an external study that found statistically significant differences between groups (typically defined by therapy vs. control or placebo) in the underlying continuous variable