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The minimal important difference of the pulmonary functional status and dyspnea questionnaire in patients with severe chronic obstructive pulmonary disease

Eloisa MG Regueiro123, Chris Burtin34, Paul Baten4, Daniel Langer34, Hans Van Remoortel34, Valéria A Pires Di Lorenzo12, Dirceu Costa15, Wim Janssens4, Marc Decramer4, Rik Gosselink34 and Thierry Troosters34*

Author Affiliations

1 Postgraduate Programme in Physiotherapy, Universidade Federal de São Carlos - UFSCar, São Carlos, Brazil

2 Special Unit of Respiratory Physiotherapy - UFSCar, São Carlos, Brazil

3 Department of Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium

4 Respiratory Rehabilitation and Respiratory Division, University Hospital Gasthuisberg, Leuven, Belgium

5 Postgraduate Programme in Physiotherapy, Universidade Nove de Julho - UNINOVE, São Paulo, Brazil

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Respiratory Research 2013, 14:58  doi:10.1186/1465-9921-14-58

Published: 25 May 2013



The modified version of the Pulmonary Functional Status and Dyspnea Questionnaire (PFSDQ-M) is used in patients with COPD to obtain information about their functional status. It consists of 3 components (change in activities, dyspnea and fatigue) ranging from 0 to 100 and has been shown to be responsive following pulmonary rehabilitation (PR). The interpretation of changes in PFSDQ-M score after an intervention is difficult in the absence of the minimal important difference (MID) of the PFSDQ-M. This study aims at investigating the MID of the PFSDQ-M.


We enrolled 301 patients with COPD (FEV1 42 ± 15%pred) that completed the PFSDQ-M before and after a 3-month PR program (∆Chronic Respiratory Disease Questionnaire (CRDQ) +16 ± 12 points, ∆Six-minute walking distance (6MWD) +47 ± 89 m, both p < 0.001). An anchor-based approach consisted of calculating the correlation between the ∆PFSDQ-M and anchors with an established MID (∆CRDQ and ∆6MWD). Linear regression analyses were performed to predict the MID from these anchors. Secondly several distribution-based approaches (Cohen’s effect size, empirical rule effect size and standard error of measurement method) were used.


Anchor-based estimates for the different PFSDQ-M-components were between −3 and −5 points based on CRDQ score and −6 (only calculated for change in activities) based on 6MWD. Using the distribution-based methods, the estimates of MID ranged from −3 to −5 points for the different components.


We concluded that the estimate of MID of the PFSDQ-M after pulmonary rehabilitation corresponds to a change of 5 points (range - 3 to −6) in each component in patients with severe COPD.

Minimal important difference; PFSDQ – Pulmonary Functional Status and Dyspnea Questionnaire; COPD – Chronic Obstructive Pulmonary Disease; Pulmonary rehabilitation; Funtional status; Symptoms