170 Chapter 8 was based on recent diagnostic guidelines and defined by either a reference standard (e.g., pneumothorax) or a composite reference (e.g., pneumonia). For patients not fulfilling one of these 26 definite diagnostic labels, we defined six additional diagnostic categories: thoracic pain of unknown origin, dyspnoea of unknown origin, fever of unknown origin, other thoracic pathology, extrathoracic pathology, and no pathology. We devised decision rules to define cases with signs of complexity (such as empyema, suspicion of a radiation pneumonitis, or a possible primary episode of interstitial lung disease). Assessors In a pilot study in randomly selected OPTIMACT trial participants we found that medical students using our diagnostic handbook agreed in only 32 out of 75 cases (43%). We therefore devised a strategy where cases in which students disagreed on the diagnosis were additionally assessed by a resident. If the medical students and the resident could not reach consensus, a final assessment was made by an expert panel of medical specialists. The students were paired from a pool of six medical students. All students had a Bachelor’s degree in Medicine. The residents (either TvE or MK) had at least one year of clinical experience as a physician. The expert panel consisted of four medical specialists: a chest radiologist, an internist, a pulmonologist and a cardiologist. All experts had at least three years of experience in their field. None of them was a member of the research team. All observers were trained in the use of the diagnostic handbook using case vignettes. Study design All cases were assessed in a structured approach based on a review of all clinical, radiological and microbiological data available after 28 days of follow-up. Study participants could have more than one diagnosis; we did not make a distinction between primary and secondary diagnoses. Only the clinical condition that was the reason for the current ED presentation was labelled. Each case was independently assessed by two medical students using data present in the electronic health record (EHR) (step 1)(Figure 1). Cases meeting the predefined criteria of complexity were directly referred to the expert panel if agreed upon by the students. If there was total agreement on all diagnostic labels, the participant was classified accordingly. If not, the case was additionally assessed by a resident who did not know the assessment of the students. The two students and the resident then discussed the case in a consensus meeting (step 2). During the meeting, a chair (a member of the research team) introduced the case, led the discussion, kept track of time and ensured consistency of assessments by keeping a log. If consensus was reached within ten minutes, the case was classified accordingly. If consensus could not be reached, or the case was deemed too complex, it was referred to the expert panel (step 3). Two members of the expert panel (the internist and the pulmonologist) were unaware of previous assessments and received paper vignettes, which they assessed individually. The cardiologist only received those cases where at least one cardiologic label was assigned or the additional diagnostic category “thoracic pain of unknown origin” or “other thoracic pathology” was assigned. The cardiologist then provided feedback in
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