Table 4.

Computing the predicted risk score.

As an example, suppose a 50-year old male patient presents to the clinic with disease confined to the small bowel. His total HBI score is 3 with a stool frequency of two per day, he is currently taking 5-ASA, and does not have a fistula, stricture, or definite abdominal mass. The clinician would now like to predict the risk of surgery within the next 2 years. Start by plugging these values into the equation for the linear predictor. lp = -3.51 [Intercept] + [50 – 45; age, years]*[- 2.5*10–3] + [1; male]*[0.36] + [1 point; HBI subtract stools/day]*[0.22] + [2 stools/day]*[6.8*10–2] + [1; small bowel only]*[0.48] + [0; antimetabolite use]*[-0.42] + [1; 5-ASA use]*[-0.55] + [0; fistula, abscess, abdominal mass]*[1.57] + [1 point; HBI subtract stools/day]*[2 stools/day]*[-1.7*10–2] = -2.8175 ≈ -2.82. Now convert the linear predictor into percent risk. Risk = 100% * 1 / [1 + exp[-lp]] = 5.6% [expected risk is approximately 5.6%].

HBI, Harvey-Bradshaw Index; 5-ASA, 5-aminosalicylate.