Chronic diarrhoea: a methodologic basis for its apparent heterogeneity.

The etiologic and epidemiologic patterns of chronic diarrhoea vary extensively between studies. While undoubtedly some of this heterogeneity reflects the complexity of the disease entity, inconsistencies in methodology between studies may result in some of the variation. To illustrate this problem we examined 44 papers on chronic diarrhoea for comparability of the age range of subjects under study and for the use of standardized definitions of 'chronic' and 'diarrhoea'. There was wide variation in the age ranges examined, extending from two weeks to 91 years. No definition or description of 'diarrhoea' was provided in 13 (30%) studies while 'chronic' remained undefined or undescribed in 11 (25%) papers. Among the 14 (32%) studies providing a definition of 'diarrhoea', four different sets of criteria were used and among the 22 (50%) papers defining 'chronic', eight different definitions were employed.