Subjective differentiation of normal and pathological bronchi on thin-section CT: impact of observer training

The effect of observer training on sensitivity, specificity and interobserv er agreement in the differentiation between normal and pathological bronchi on computed tomography (CT) was studied. The wall thickness of bronchi with normal walls and with pathologically thi ckened walls were subjectively scored by three independent observers before and after a training period of 2 weeks. Sensitivity, specificity and inter observer agreement were calculated for reading sessions before and after tr aining. Increase and decrease in agreement after training were determined. There was a statistically significant difference (p=0.001) between objectiv ely measured wall thickness of normal and pathological bronchi, both for re ference bronchi and for bronchi used for reading sessions. While training i ncreased interobserver agreement, it had no effect on sensitivity (0.46 ver sus 0.44 after training) and specificity (0.71 versus 0.72 after training) in detecting pathological bronchi. Increased agreement after training was s ignificantly (p=0.001) more frequent than decreased agreement. There is a discrepancy between the effect of training on interobserver agre ement and on sensitivity and specificity in the subjective differentiation between normal and pathological bronchi. Interobserver agreement alone is n ot a reliable indicator of a beneficial effect of training in the evaluatio n of this parameter.