The Severe Asthma Questionnaire: sensitivity to change and minimal clinically important difference (MCID)

The Severe Asthma Questionnaire (SAQ) is a validated measure of the health-related quality of life of people living with severe asthma [1]. The minimal clinically important difference (MCID) of the SAQ has not been calculated. The MCID is useful for representing clinical as opposed to statistical significance. There are two main ways of calculating the MCID. Distribution methods define the MCID in terms of the relationship between the distribution of scores and mean change score. These methods are purely statistical and the relationship and formulae that constitute the MCID is determined by convention. By contrast, the anchor method [2] defines the MCID in terms of an independent anchor or criterion. When the anchor is the patient's perception of a just noticeable difference in their condition, then the anchor method has two advantages over the distribution method. First, the MCID is defined by a criterion and, therefore, has criterion validity rather than being only a convention. Second, the MCID is defined in terms of the patient's perception of treatment, and the patient's perception of their treatment is recognised as being an important outcome for clinical decision-making [2]. In this letter we present the MCID of the SAQ using the anchor method. The Severe Asthma Questionnaire (SAQ) is sensitive to change and clinically significant improvement was detected within 4 weeks of starting biologic therapy. The MCID of the SAQ is 0.5 and of the SAQ-global is 11. https://bit.ly/3poJqcG