Editor,—Geboes et aldescribed a grading system for inflammation in ulcerative colitis and carried out rigorous assessment of the reproducibility of this system ((2000) Gut 47:404–9.OpenUrlCrossRefPubMedWeb of Science). This is a very useful study which fills a void in the histopathology assessment of ulcerative colitis. However, now that this system has been described, its use in clinical practice and clinical trials needs to be considered.

Many of the features that Geboes et alhave used in their grading system are described as continuous spectra—for example, chronic inflammation assessed from no increase through to marked increase—but are divided into discrete groups (for example, mild, moderate, marked). This means that these features are ordinal categorical variables rather than continuous real numbers—that is, they have a numerically labelled order but the distance between adjacent numbers will not be the same through the whole range and there are no non-integer values.1 The consequences of this are that these grades cannot be used in processes which require continuous variables, such as linear regression.2 The authors already seem to have made this mistake themselves as they give …

K Geboes, Department of Pathology, University Hospital, KU Leuven, Minderbroedersstraat 12, 3000 Leuven, Belgium. Karel.Geboes{at}uz.kuleuven.ac.be