Predicting the Crohnʼs disease activity index from the harvey-bradshaw index

BackgroundThe Crohn's Disease Activity Index (CDAI) was developed in the 1970s to assess the degree of illness in individuals with Crohn's disease and has since been used widely in clinical trials of the condition. The Harvey-Bradshaw Index (HBI) is a simplification of the CDAI, designed to make data collection and computation easier. It is purported, on the basis of a 0.93 correlation coefficient, to give "essentially the same information." However, correlation is an incomplete way to assess sameness, and this study aimed to develop a method for predicting CDAI from HBI values, including relevant prediction limits.