The daily diary and the questionnaire are not equivalent for the evaluation of bowel habits.

Background: It is unclear whether questionnaires and diary cards, which are widely used to collect data on bowel habits, provide analogous information.

Aims: We verified the concordance between the data provided by a daily diary and a retrospective questionnaire.

Methods: A 4-week diary (DIARY) concerning bowel habits was compiled by 221 subjects. They were also asked to fill out a questionnaire on their bowel habits before (BEF) and after (AFT) the diary period.

Results: Concerning bowel movements, no significant difference was detected in the concordance between BEF and DIARY (rho: 0.80), AFT and DIARY (rho: 0.84), or BEF and AFT (rho: 0.84). The mean concordance in the other defecation-related parameters between BEF and DIARY (K: 0.62) and between DIARY and AFT (K: 0.63) were both significantly lower than that seen between BEF and AFT (K: 0.80; p<0.01).

Conclusion: A considerable discrepancy between the two methods of assessment was found. The higher concordance between BEF and AFT than between DIARY and AFT regarding defecation-related parameters suggests that when a subject recalls events, even those from the recent past, he/she tends to generalize, reporting more or less the same data for different periods of time. These two instruments cannot be viewed as interchangeable, and their inherent differences must be taken into account when deciding which one to employ in different settings.