Construction and validation of a risk-screening questionnaire for the investigation of recurrent airway obstruction in epidemiological studies of horse populations in Great Britain

Recurrent airway obstruction (RAO) is an environmental respiratory disease affecting horses. A risk-screening questionnaire (RSQ) for RAO would provide a useful tool to investigate the epidemiology of the disease in horses; our aim in this study was to construct and validate such an instrument. Guidance for what questions to include in the RSQ came from three processes: a review of the scientific literature, a survey of equine practitioners in the UK and a consultation with 19 experts using a modified Delphi technique. The latter consultation consisted of two rounds; agreement amongst the experts increased between the rounds. The quantitative outputs provided estimates of the probabilities of a horse having RAO for each particular piece of historical information or clinical sign. The RSQ for RAO was a short questionnaire for completion by horse owners regarding the horse, its health and its management. The likelihood of a horse having RAO (the RAO score) was calculated from a completed RSQ by combining the relevant estimated probabilities. The RSQ was validated against a reference standard of a veterinary diagnosis including respiratory cytology. This was achieved by inviting veterinary surgeons (residing in Great Britain who had taken part in the practitioner survey, and who had indicated that they used respiratory cytology in the diagnosis of respiratory cases) to participate. During 2003 and 2004 these veterinary surgeons returned RSQs for 40 cases that underwent investigation of the respiratory tract and 40 controls; 18 of the cases were given a final diagnosis of RAO. A receiver-operating characteristic (ROC) curve was used to select a positive cut-off of 0.87 for the RSQ for RAO. This suggested that the RSQ had a sensitivity of 0.83 (95% confidence interval = 0.59–0.96) and specificity of 0.85 (0.74–0.93) for the diagnosis of apparent RAO (compared to all other diagnoses).