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. Footnotes This manuscript has recently been accepted for publication in the European Respiratory Journal . It is published here in its accepted form prior to copyediting and typesetting by our production team. After these production processes are complete and the authors have approved the resulting proofs, the article will move to the latest issue of the ERJ online. Please open or download the PDF to view this article. Conflict of interest: Dr. Lindner has nothing to disclose. Conflict of interest: Dr. Masoli reports grants from GlakoSmithKline, personal fees from Astra Zeneca, personal fees from Novartis, during the conduct of the study. Conflict of interest: Mr. Lanario reports grants from GSK, during the conduct of the study; personal fees from Novartis, outside the submitted work. Conflict of interest: Dr. Hyland reports grants from GSK, during the conduct of the study; personal fees from GSK, outside the submitted work. Conflict of interest: Dr. Menzies-Gow reports grants and personal fees from Astra Zeneca, personal fees from Novartis, personal fees and non-financial support from Teva, personal fees from Glaxo SmithKline, personal fees from Sanofi, personal fees from Roche, personal fees from Vectura, outside the submitted work. Conflict of interest: Dr. Mansur reports grants, personal fees, non-financial support and other from NAPP, Cheisi, Astrazeneca, GSK, Sanofi, Teva, GSK, , outside the submitted work. Conflict of interest: Dr. Allen reports personal fees from Astra Zenaca, personal fees from GSK, personal fees and non-financial support from Teva, outside the submitted work. Conflict of interest: Dr. Dodd has nothing to disclose. Conflict of interest: Dr. Hayes has nothing to disclose. Conflict of interest: Dr. Valderas has nothing to disclose. Conflict of interest: Sarah E Lamb was on the Health Technology Assessment (HTA) Additional Capacity Funding Board, HTA End of Life Care and Add-on Studies Board, HTA Prioritisation Group Board and the HTA Trauma Board. Conflict of interest: Dr. Jones reports grants from Glaxo Smith Kline, during the conduct of the study; grants, personal fees and non-financial support from Astra Zeneca, personal fees and non-financial support from Boehringer Ingelheim, grants, personal fees and non-financial support from Glaxo Smith Kline, personal fees and non-financial support from Novartis, personal fees and non-financial support from Nutricia, from null, outside the submitted work.