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Original Research |

Estimating a Minimally Important Difference in Pulmonary Arterial Hypertension Following Treatment With Sildenafil

Claire Gilbert, MSc*; Martin C. J. Brown, MSc; Joseph C. Cappelleri, PhD; Martin Carlsson, MS; Stephen P. McKenna, PhD
Author and Funding Information

*From PGRD (Ms. Gilbert), Pfizer Ltd., Sandwich, Kent, UK; Global Health Outcomes Research (Mr. Brown), UCB Celltech, Slough, Berkshire, UK; Pfizer Inc (Dr. Cappelleri and Mr. Carlsson), Groton, CT; and Galen Research (Dr. McKenna), University of Central Lancashire, Manchester, UK.

Correspondence to: Claire Gilbert, PGRD, Pfizer Ltd., Ramsgate Rd, Sandwich CT13 9NJ, UK; e-mail: claire.gilbert@pfizer.com

*Data are presented as No. (%) or mean ± SD.

*ES 0.3 (small to moderate); ES 0.5 (moderate); ES 0.8 (large); 1 − SEM = change of 1 SEM at baseline; 1 − Sdiff = change of 1 Sdiff; 1.96 − SEM = change of 1.96 SEM at baseline; 1.96 − Sdiff = change of 1.96 Sdiff.

†Mean of all MID estimations.

Ms. Gilbert is an employee of Pfizer Ltd., Dr. Cappelleri and Mr. Carlsson are employees of Pfizer Inc, Mr. Brown is a former employee of Pfizer Ltd., and Dr. McKenna was an unpaid consultant on this project. There are no other conflicts of interest.

This study was funded by Pfizer Ltd., Sandwich, Kent, UK.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml).


Ms. Gilbert is an employee of Pfizer Ltd., Dr. Cappelleri and Mr. Carlsson are employees of Pfizer Inc, Mr. Brown is a former employee of Pfizer Ltd., and Dr. McKenna was an unpaid consultant on this project. There are no other conflicts of interest.

Ms. Gilbert is an employee of Pfizer Ltd., Dr. Cappelleri and Mr. Carlsson are employees of Pfizer Inc, Mr. Brown is a former employee of Pfizer Ltd., and Dr. McKenna was an unpaid consultant on this project. There are no other conflicts of interest.

This study was funded by Pfizer Ltd., Sandwich, Kent, UK.

This study was funded by Pfizer Ltd., Sandwich, Kent, UK.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml).

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml).


Chest. 2009;135(1):137-142. doi:10.1378/chest.07-0275
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Background:  No guidelines exist to help physicians determine whether functional and health-related quality of life (HRQoL) changes observed following treatment of patients with pulmonary arterial hypertension (PAH) represent important benefits. These analyses were undertaken to help define a minimally important difference (MID) in exercise capacity, measured by the 6-min walk distance (6MWD), and HRQoL, measured by the Short Form-36 (SF-36) questionnaire in patients with PAH.

Patients and methods:  Data from a 12-week sildenafil study in patients with PAH were used to calculate MIDs for 6MWD and the SF-36 physical functioning, role-physical, social functioning, and vitality scales using effect size, SEM, and SE of the difference approaches. Data from all patients enrolled into the treatment groups in the study were included.

Results:  A range of plausible MID estimates, including a score change for SF-36 scales and a change in distance walked in meters for 6MWD, were generated for each end point. Mean values were calculated for each outcome and recommended as MIDs for each parameter. Based on these computations, the mean MIDs for the SF-36 physical functioning, role-physical, social functioning, and vitality scales and for 6MWD were 13, 25, 21, and 15 points, and 41 m, respectively.

Conclusions:  This is the first clinical investigation to estimate MIDs for key SF-36 domains and 6MWD in patients with PAH and provides a much needed metric for interpreting the level of change in patients with PAH against which other treatments and trials can be measured.


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