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Physicians take both diagnosis and prognosis into account when allocating treatment. However, by "prognosis" physicians usually imply a somewhat vague impression concerning large groups of patients. One possible task for decision support studies is to design and construct systems that accurately predict individual patient prognoses. The authors constructed and tested such systems in three areas of medicine (inflammatory bowel disease, upper gastrointestinal tract hemorrhage, and acute chest pain). In each area, the individual patient's symptoms were compared with a computer-held database of information via a Bayesian analysis, prior and conditional probabilities being derived from large-scale real-life surveys. Prospective trials designed to test these predictive systems by reference to test series comprising over 4,000 patients indicate that a firm prognostic prediction can generally be made; where made, the accuracy of prediction is over 90%. Ways in which this type of prediction may be of clinical value are discussed.

Summary:We describe the use of activity indices during a prospective trial of 91 patients with active Crohn's disease. Data were recorded by experienced physician investigators in four centres, and several activity indices were compared. The indices studied included modifications of the Crohn's Disease Activity Index (CDAI), the Dutch Activity Index, and the European SeveritylActivity Index. Correlation was made between each index, between the indices and physician's opinion, and between each index and patient progress. The correlation between indices was generally somewhat higher than that observed during a similar study in the early 1980s. Our results suggest close correlation between the variants of the CDAI, but less good correlation with the Dutch or European indices. There was also good correlation between CDAI variants and physicians' opinion, both as measured on linear analogue scale and as measured by physician action. All assessed indices correlated poorly, however, with short-term patient prognosis. New indices, or combinations of existing datasets, will be necessary to solve this problem. Key Words: Activity indicesCrohn's disease-Severity.A rapid and reliable estimation of the activity of Crohn's disease is important for managing individual patients and for conducting therapeutic trials. Unfortunately, it has proved difficult to achieve. Studies in the 1960s (1,2) showed that clinicians' intuitive assessments of severity are less than completely reliable, one study showing that three clinicians disagreed whether the patients were getting better or getting worse in almost 50% of the assessments.A natural consequence of this difficulty was the development of more formal scales and indices to measure severity or activity of Crohn's disease, such as the Crohn's Disease Activity Index (CDAI) of the National Co-operative Crohn's Disease Study (3), its modification by Harvey and Bradshaw (4) and by the World Organisation of Gastroenterology (3, as well as the original authors themselves ( 6 ) , along with other indices from Holland (7),

: We describe the use of activity indices during a prospective trial of 91 patients with active Crohn's disease. Data were recorded by experienced physician investigators in four centres, and several activity indices were compared. The indices studied included modifications of the Crohn's Disease Activity Index (CDAI), the Dutch Activity Index, and the European Severity/Activity Index. Correlation was made between each index, between the indices and physician's opinion, and between each index and patient progress. The correlation between indices was generally somewhat higher than that observed during a similar study in the early 1980s. Our results suggest close correlation between the variants of the CDAI, but less good correlation with the Dutch or European indices. There was also good correlation between CDAI variants and physicians' opinion, both as measured on linear analogue scale and as measured by physician action. All assessed indices correlated poorly, however, with short-term patient prognosis. New indices, or combinations of existing datasets, will be necessary to solve this problem.