The Asthma Control Questionnaire (ACQ)1 was developed and validated to measure the primary clinical goal of asthma management as identified by international guidelines. They indicate that to achieve good control, treatment should minimise day and night time symptoms, activity limitation, airway narrowing and rescue bronchodilator use and thus reduce the risk of life-threatening exacerbations and long-term morbidity. The importance of including all aspects of control in the assessment of individual patients was emphasised by a recent factor analysis which showed that clinical asthma is composed of distinct components which are not closely correlated with each other.6 However, in some studies it may not be possible to collect airway calibre or short-acting β2-agonists data. Previous analysis of non-clinical trial data suggested that when ACQ scores are analysed as group data, the heterogeneity of the way in which individual patients present with inadequate control is lost in the estimation of the mean and the need to measure each individual component of asthma control may become unnecessary. In this analysis, ACQ data from a clinical trial was used to evaluate the measurement properties (reliability, responsiveness, validity and interpretability), of three shortened versions of the ACQ. In addition, we have examined whether the precision and accuracy of estimating the effect of the intervention on asthma control was maintained when the two questions concerning airway calibre and short-acting β2-agonists use were omitted from the trial analysis.