Methods: Clinicians were asked for an estimation of probabilities related with the outcome of treated and not treated pulmonary tuberculosis, as well as for the toll of wrong decisions. Three ratios of the weight of forgoing a treatment in a false negative against the weight of giving a treatment to a false positive were calculated. The first was based on intuitive weights. The second was computed with estimations of probabilities of mortality and morbidity related to disease and treatment, and an intuitive weight for each of these parameters. The third was similar to the former, but literature data were used in stead of estimations for probability data. Finally, the association between experience and the difference between the intuitive and the calculated ratios was assessed.

Results: Eighty one participants from Ecuador, Laos, Nepal and Rwanda responded. The ratio of intuitive weights was 2,0 (IQR:1,0-4,0) while the ratio of calculated weight based on intuitive probabilities was 97,0 (IQR:32,8-241,8) (p<0,001). The ratio of calculated weight based on literature probabilities was 97,2 (IQR:47,3-172,9). No association (R^2=0,03) was found between experience and accuracy to estimate the weight of errors.

Conclusion: The weight of a false negative is more important than the weight of a false positive for therapeutic decisions in pulmonary tuberculosis. The ratio of the intuitively estimated weight of false negatives vs. false positives was 100 times lower than the calculated based on intuitively estimated influencing factors. Clinicians are accurate in estimating probabilities but they fail to consider them in therapeutic decisions.