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Interpreting Clinical Differences in BREAST-Q Scores

Minimal Important Difference

Cano, Stefan J. Ph.D.; Klassen, Anne F. D.Phil.; Scott, Amie M.P.H.; Alderman, Amy M.D., M.P.H.; Pusic, Andrea L. M.D., M.H.S.

Author Information
Plastic and Reconstructive Surgery: July 2014 - Volume 134 - Issue 1 - p 173e-175e
doi: 10.1097/PRS.0000000000000267
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Sir:

The BREAST-Q is a multiscale, multimodule, patient-reported outcome instrument measuring important aspects of health-related quality of life and patient satisfaction in women who undergo breast surgery.1 Its subscales have undergone extensive psychometric evaluation,2 including examinations of clinical change.3 However, to date, no minimal important difference statistics have been published. These statistics are especially important for power calculations in clinical research and therapeutic trials.4 Thus, here we present distribution-based minimal important differences (i.e., values relating to one-half of the baseline standard deviation in subscale scores, and effect sizes of 0.5)5 for the subscales that compose the BREAST-Q Augmentation Module. These minimal important difference statistics were derived from data collected within a longitudinal study of 245 women undergoing cosmetic breast augmentation. The women in this study completed the BREAST-Q before surgery and again 6 weeks and 6 months after surgery (further information is available from the authors).

Table 1 shows the statistics related to the clinical change in BREAST-Q scores. Of importance, the last two columns of Table 1 show the mean minimal important differences based on a 0.5 SD and 0.5 effect size for each of the module’s subscales. Taking the most conservative value in each instance, the mean minimal important difference equates to the following (BREAST-Q Augmentation Module): satisfaction with breasts, 8 (range, 7 to 8); psychosocial well-being, 10 (range, 8 to 11); sexual well-being, 10 (range, 9 to 10); and physical well-being, 7 (range, 2 to 11).

T1-54
Table 1:
BREAST-Q Subscale Mean Scores (Measurements), Standard Deviations, Effect Sizes, and Minimal Important Difference (n = 213–216)*

One of the key clinical benefits of using Rasch Measurement Theory methods to develop the BREAST-Q is that we have a good understanding of the empirical item order across each subscale.2 Thus, the items (representing important clinical issues) that are associated with every possible subscale score (or measurement) are known. This benefit means that we are able to link the items directly to minimal important differences. For example, based on the BREAST-Q Augmentation Module satisfaction with breasts subscale, Figure 1 and Table 2 show three simulated example scenarios that illustrate change scores: the first not exceeding a minimal important difference (from 61 to 67; red line); the second exceeding 1 minimal important difference (from 70 to 79; blue line); and the third exceeding 2 minimal important difference values (from 40 to 61). Specifically, the scores can be translated into key issues as described by the BREAST-Q. Thus, women who move from a score of 61 to 67 go from being satisfied with the “position” and proximity of their breasts when not wearing a bra and “how their bras fit,” to being very satisfied with the “size,” “firmness,” and how “natural” their breasts appear. However, as described, this improvement in score does not exceed the minimal important difference. Women who change from a score of 70 to a 79 move from being very satisfied with “cleavage,” how “natural” their breasts are, and “how they appear in the mirror clothed” to being very satisfied with the proximity, feeling of the breasts, and “how they appear in the mirror unclothed.” This improvement signifies a minimal important difference at the high end of this subscale. Finally, at the lower end of the scale, moving from a 40 to a 61 (over double the minimal important difference) is associated with the difference between being dissatisfied with the “shape” of the breast, how the breast size “matches” the rest of their body, and “how bras fit” to being satisfied with the “position” and proximity of their breasts when not wearing a bra and “how their bras fit.”

T2-54
Table 2:
BREAST-Q Augmentation Module Satisfaction with Breasts Subscale
F1-54
Fig. 1:
BREAST-Q Augmentation Module satisfaction with breasts subscale. Three examples of change scores signifying less than a minimal important difference (red line), exceeding 1 minimal important difference (blue line), and exceeding 2 minimal important differences (green line).

As we have previously proposed, the ability to provide qualitative statements to subscale scores, and now link these to important differences in scores, begins to provide a solid foundation for the clinical interpretation of the BREAST-Q.2 Interpretability is the cornerstone to successful use of patient-reported outcome instruments in individual clinical care, comparative effectiveness research, and regulator efforts.4

DISCLOSURE

The BREAST-Q is jointly owned by the Memorial Sloan-Kettering Cancer Center and the University of British Columbia. Stefan J. Cano, Ph.D., Anne F. Klassen, D.Phil., and Andrea L. Pusic, M.D., M.H.S., are co-developers of the BREAST-Q and, as such, receive a share of any license revenues based on the inventor sharing policies of these two institutions. The BREAST-Q is provided free of charge for academic research and use in clinical practice by health care providers with individual patients. The scoring software, Q-Score, is also offered free of charge to all BREAST-Q users. The BREAST-Q is available at www.BREAST-Q.org.

Stefan J. Cano, Ph.D.

Clinical Neurology Research Group

Plymouth University Peninsula

School of Medicine and Dentistry

Plymouth, United Kingdom

Anne F. Klassen, D.Phil.

Faculty of Health Sciences

McMaster University

Hamilton, Ontario, Canada

Amie Scott, M.P.H.

Plastic and Reconstructive Surgery

Memorial Sloan-Kettering Cancer Center

New York, N.Y.

Amy Alderman, M.D., M.P.H.

Swan Center for Plastic Surgery

Atlanta, Ga.

Andrea L. Pusic, M.D., M.H.S.

Plastic and Reconstructive Surgery

Memorial Sloan-Kettering Cancer Center

New York, N.Y.

REFERENCES

1. Pusic A, Klassen A, Scott A, Klok J, Cordeiro P, Cano S. Development of a new patient reported outcome measure for breast surgery: The BREAST-Q. Plast Reconstr Surg. 2009;124:345–353
2. Cano S, Klassen A, Scott A, Pusic A. A closer look at the BREAST-Q. Clin Plast Surg. 2013;40:287–296
3. McCarthy CM, Klassen AF, Cano SJ, et al. Patient satisfaction with postmastectomy breast reconstruction: A comparison of saline and silicone implants. Cancer. 2010;116:5584–5591
4. U.S. Food and Drug Administration. . Patient reported outcome measures: Use in medical product development to support labeling claims (online). http://www.fda.gov/downloads/Drugs/Guidances/UCM193282.pdf.
5. Norman GR, Sloan JA, Wyrwich KW. Interpretation of changes in health-related quality of life: The remarkable universality of half a standard deviation. Med Care. 2003;41:582–592

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