Teaching X-ray interpretation: selecting the radiographs by the target population Kathy Boutis, 1 Martin Pecaric 2 & Martin Pusic 3 CONTEXT The unbiased selection of images representing a spectrum of diagnostic difficulty is an important first step in designing effective assessment and teaching interventions for X-ray interpretation. OBJECTIVES This study aimed to develop a scale that would reliably differentiate more difficult X-rays from those that are easier to interpret. METHODS After pilot testing, an X-ray diffi- culty scale (XRDS) was developed. Raters of different learner levels from two universities were presented with 20 chest X-rays (CXRs) and asked to read them and then to answer the scale questions that would help to differ- entiate the level of difficulty of interpretation of each film. Reliability of the scale was eval- uated. Face validity of the scale was assessed and the construct validity of two hypotheses was tested. RESULTS The final scale consisted of five questions in which a given X-ray could score from ) 10 (most difficult) to + 10 (easiest to interpret) by a single rater. Raters included 53 medical students, 10 paediatric residents and 10 emergency staff. The scale demonstrated excellent internal consistency (r = 0.94), inter- rater reliability (r= 0.95) and overall reliability (r= 0.90) in medical students. Construct valid- ity testing demonstrated good correlation (r = 0.72) between diagnostic accuracy and mean XRDS score. Mean scores on the scale were significantly lower (indicating that CXRs were more difficult to interpret) for students than for resident and staff doctors (P < 0.0001). CONCLUSIONS The scale developed in this study serves as a reliable and valid tool for categorising CXRs according to diagnostic difficulty, which reduces the bias inherent in the process of selecting radiographs by expert opinion alone. optimising teaching Medical Education 2009: 43: 434–441 doi:10.1111/j.1365-2923.2009.03311.x 1 Department of Pediatrics, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada 2 Contrail Consulting Services, Toronto, Ontario, Canada 3 Department of Pediatrics, Morgan Stanley Children’s Hospital of New York Presbyterian, Columbia University, New York, New York, USA Correspondence: Kathy Boutis, 555 University Avenue, Toronto, Ontario M5G 1X8, Canada. Tel: 00 1 416 813 8982; Fax: 00 1 416 813 5043; E-mail: boutis@pol.net 434 ª Blackwell Publishing Ltd 2009. MEDICAL EDUCATION 2009; 43: 434–441