Evaluating the “Good Death” Concept from Iranian Bereaved Family

O R I G I N A L R E S E A R C H
Estimating Minimally Important
Differences for the Worst Pain Rating of
the Brief Pain Inventory–Short Form
Susan D. Mathias, MPH, Ross D. Crosby, PhD, Yi Qian, PhD, Qi Jiang, PhD, Roger Dansey, MD, and
Karen Chung, PharmD, MS
Certain outcomes, such as pain, are only
known to patients and therefore are best
reported through a patient-reported outcome
(PRO) measure. To be clinically useful, a
PRO measure must be valid, reliable, and responsive
to change. In addition, interpretation of data
from PRO measures is aided by estimation of the
minimally important difference (MID). The
MID is the smallest difference in a PRO measure
that a patient would consider beneficial or detrimental.
Although the MID may not affect the
patient’s clinical treatment or care, patients are
the primary stakeholders in the evaluation of
PROs, and patient-perceived differences are particularly
relevant in advanced stages of disease
where palliation may be the focus of treatment. 1
The MID may be estimated through distribution-based
methods and/or anchor-based methods.
Distribution-based methods are based on the
distribution of the data. Examples of distributionbased
methods include effect size measures, the
standard error of measurement (SEM), one-half
times the standard deviation, and the responsiveness
index. 2,3 Anchor-based methods are based
on the association between the PRO measure
and an interpretable external measure, such as a
global rating of change or a response to treatment.
These methods may result in somewhat
From Health Outcomes Solutions, Winter Park, Florida; Biomedical
Statistics and Methodology, Neuropsychiatric Research
Institute, Fargo, North Dakota; Global Biostatistics,
Global Development, and Global Health Economics, Amgen,
Inc., Thousand Oaks, California.
Manuscript received June 25, 2010; Accepted December 3,
2010.
Correspondence to: Susan D. Mathias, Health Outcomes
Solutions, PO Box 2343, Winter Park, FL 32790; telephone:
(407) 643-9016; fax: (866) 384-0194; e-mail: smathias@
healthoutcomessolutions.com
J Support Oncol 2011;9:72–78 © 2011 Elsevier Inc. All rights reserved.
doi:10.1016/j.suponc.2010.12.004
Abstract The Brief Pain Inventory–Short Form (BPI-SF) is widely used for
assessing pain in clinical and research studies. The worst pain rating is often
the primary outcome of interest; yet, no published data are available on its
minimally important difference (MID). Breast cancer patients with bone
metastases enrolled in a randomized, double-blind, phase III study comparing
denosumab with zoledronic acid for preventing skeletal related
events and completed the BPI-SF, FACT-B, and EQ-5D at baseline, week 5,
and monthly through the end of the study. Anchor- and distribution-based
MID estimates were computed. Data from 1,564 patients were available.
Spearman correlation coefficients for anchors ranged from 0.33–0.65.
Mean change scores for worst pain ratings corresponding to one-category
improvement in each anchor were 0.26–1.04 for BPI-SF current pain, �1.40
to �2.42 for EQ-5D Index score, 1.71–1.98 for EQ-5D Pain item, �2.22 to
�0.51 for FACT-B TOI, �1.61 to �0.16 for FACT-G Physical, and �1.31 to
�0.12 for FACT-G total. Distribution-based results were 1 SEM � 1.6, 0.5
effect size � 1.4, and Guyatt’s statistic � 1.4. Combining anchor- and
distribution-based results yielded a two-point MID estimate. An MID estimate
of two points is useful for interpreting how much change in worst
pain is considered clinically meaningful.
different estimates, and no particular estimate is
considered the most valid. 2–4 Therefore, researchers
are encouraged to use more than one
method and to present a range of MID estimates.
A frequently used PRO measure for the assessment
of pain is the Brief Pain Inventory–Short
Form (BPI-SF). The foundation of the BPI-SF is
the Wisconsin Brief Pain Questionnaire, which
was developed over 25 years ago based on interviews
with cancer patients, expert opinion, and
then-current psychometric standards. 5 Over
time, the Wisconsin Brief Pain Questionnaire
evolved into the Brief Pain Inventory, which was
later reduced to a shorter version, the BPI-SF.
Today, the BPI-SF is the standard for clinical and
research use. It has been used in over 400 studies,
including psychometric evaluations and clinical
applications with a wide range of conditions
72 www.SupportiveOncology.net THE JOURNAL OF SUPPORTIVE ONCOLOGY