Purpose: Because of the rarity of intracranial hemorrhage (ICH), the most dreaded complication of the pediatric disorder of idiopathic thrombocytopenic purpura (ITP), there are few data to guide clinical practice. The purpose of this study was to find where the core disagreement lay between those who would treat children on initial presentation and those who would not; to determine whether each group's explicitly preferred policy was consistent with the conclusion of a decision based on their detailed perceptions, and to identify key variables in each perspective's model.

Methods: A decision model (decision tree in TreeAge) was constructed in collaboration with pediatric hematologist experts, and a detailed questionnaire was presented to a nationally representative committee of 25 pediatric hematologists. Enough data was elicited to specify a full model for each respondent.

Results: 19 (76%) experts responded; based on preferred initial treatment, there were 12 treaters and 7 non-treaters. Out of 60 variables, there was statistically significant differences on 3 variables: the relative risk reduction of ICH by the three treatments (Anti-D: treaters 64% vs non-treaters 27% (P .012, min Bayes Factor against null hypothesis 13); IVIG: treaters 76% vs non-treaters 33% (P .0018, BF 69); steroids: treaters 71% vs non-treaters 28% (P .001, BF 120)). A non-inferiority study would require 11,000 patients to change the opinion of treaters to non-treaters. There was agreement on values: Median number needed to treat (NNT) to avoid ICH was 100; median NNT to avoid treatment side effects was < 1. The derived NNT of treatment for treaters was 10,000; for non-treaters, 30,000. For treaters, although anti-D was the reported preferred treatment, the steroids strategy was cost saving and anti-D conferred an incremental cost effectiveness ratio of $10.5 million.

Conclusion: Decision-analytically naïve physicians provided enough data to specify complete individual models. The disagreement among these investigators concerns probabilities and not values. These decision-analytically results helped these investigators to clarify their goals on a formal basis