Evaluation of the minimal important difference for the feeling thermometer and the St. George's Respiratory Questionnaire in patients with chronic airflow obstruction

Schünemann, Holger J; Griffith, Lauren; Jaeschke, Roman; Goldstein, Roger; Stubbing, David; Guyatt, Gordon H

doi:10.1016/S0895-4356(03)00115-X

« Previous Next »Journal of Clinical Epidemiology
Volume 56, Issue 12 , Pages 1170-1176, December 2003

Evaluation of the minimal important difference for the feeling thermometer and the St. George's Respiratory Questionnaire in patients with chronic airflow obstruction

Holger J Schünemann
- Department of Medicine, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, 462 Grider Street, Buffalo, NY 14215, USA
- Department of Social and Preventive Medicine, School of Public Health and Health Professions, State University of New York at Buffalo, 3435 Main Street, Buffalo, NY 14214, USA
- Department of Clinical Epidemiology and Biostatistics, Health Sciences Centre, McMaster University, Room 2C12, 1200 Main Street West, Hamilton, ON L8N 3Z5, Canada
- Corresponding author. Tel.: 905-525-9140; fax: 905-577-0017.
Lauren Griffith
- Department of Clinical Epidemiology and Biostatistics, Health Sciences Centre, McMaster University, Room 2C12, 1200 Main Street West, Hamilton, ON L8N 3Z5, Canada
Roman Jaeschke
- Department of Clinical Epidemiology and Biostatistics, Health Sciences Centre, McMaster University, Room 2C12, 1200 Main Street West, Hamilton, ON L8N 3Z5, Canada
Roger Goldstein
- Westpark Healthcare Centre, University of Toronto, 82 Buttonwood Avenue, Toronto, ON M6M 2J5, Canada
David Stubbing
- ^eDepartment of Medicine, Health Sciences Centre, McMaster University, Room 2C12, 1200 Main Street West, Hamilton, ON L8N 3Z5, Canada
- Deceased.
Gordon H Guyatt
- Department of Clinical Epidemiology and Biostatistics, Health Sciences Centre, McMaster University, Room 2C12, 1200 Main Street West, Hamilton, ON L8N 3Z5, Canada
- ^eDepartment of Medicine, Health Sciences Centre, McMaster University, Room 2C12, 1200 Main Street West, Hamilton, ON L8N 3Z5, Canada

Accepted 6 December 2002.

Abstract

Background and objective

The chronic respiratory questionnaire (CRQ), the St. Georges Respiratory Questionnaire (SGRQ), and the feeling thermometer (FT) evaluate change in health-related quality of life (HRQL) in patients with chronic airflow limitation (CAL). Although the interpretability, and in particular the minimal important difference (MID) in score changes, is well established for the CRQ, this is not the case for the SGRQ and FT. The objective of our study is to explore the interpretation of the SGRQ and FT.

Methods

We analyzed data from 84 patients who completed the CRQ, SGRQ, and FT before beginning pulmonary rehabilitation and 3 months later. We calculated correlations between the four CRQ domains (dyspnea, fatigue, emotional function, and mastery) and the three SGRQ domains (symptoms, activities, and impact), the SGRQ total score, and the FT. When Pearson's correlations were ⩾0.5, we constructed regression equations and used the slope to calculate the change in SGRQ and FT score that corresponded to a change in CRQ score of 0.5 (the MID). Having established MID for SGRQ we than used a similar approach to examine the relation between the SGRQ and FT results.

Results

Comparison with the CRQ dyspnea domain suggested the MID in SGRQ total score is approximately 3.05 with a 95% confidence interval (95% CI) ranging from 0.39 to 5.71 and a change of 5.67 (95% CI 3.43–7.92) represents a moderate change (1.0 on the CRQ dyspnea domain). The MID for the FT based on the CRQ fatigue domain was 6.1 (95% CI 1.87–10.28). The FT MID based on the SGRQ activities domain, impacts domain, and total score were, respectively, 7.4 (95% CI 3.44–11.35), 5.6 (95% CI 1.6–9.64), and 5.9 (95% CI 1.97–9.78).

Conclusion

An MID for the SGRQ approximates the previously suggested estimate of 4 on a scale of 0 to 100. The MID for the FT in patients with CAL is approximately 5 to 8 units on the 0 to 100 scale. These MID estimates should facilitate interpretation of clinical trials in which outcome measures include the SGRQ or FT.

Keywords: Quality of Life, Visual analog scale, Feeling thermometer, Interpretability, Respiratory rehabilitation, COPD, Minimal important difference