Els van de Vijver

71 Figure 3 I Decision curves for four diagnostic strategies to predict IBD. The default strategies were to perform endoscopy in all patients or in none. A diagnostic strategy is clinically useful if it has a greater net benefit than the default strategies. Strategy 3 (symptoms + calprotectin) provided greater net benefit than strategy 2 (symptoms + blood markers) up to a risk threshold of 50%. When the risk threshold was 50 to 70%, strategy 2 had greater net benefit. The basic model (symptoms only) provided hardly any greater net benefit than performing endoscopy in all patients, or alternatively, performing endoscopy in no one. Box. How to read figure 3? Assume that a clinician does not want to expose more than 2 children to endoscopy to detect one case with IBD. In this instance the “harm-to-benefit” ratio is 1:1 (or a risk threshold of 50%). At this risk threshold the net benefit of 0.10 means that strategy 4 leads to exposing 100 per 1000 children at risk, with all of the exposed having IBD. Test strategies to predict IBD 71