VU Research Portal
Interpreting change scores for pain and functional status in low back pain: towards
international consensus regarding minimal important change
Ostelo, R.W.J.G.; Deyo, R.A.; Stratford, P.; Waddell, G.; Croft, P.; Von Korff, M.; Bouter,
L.M.; de Vet, H.C.W.
published in
Spine
2008
DOI (link to publisher)
10.1097/BRS.0b013e31815e3a10
document version
Publisher's PDF, also known as Version of record
Link to publication in VU Research Portal
citation for published version (APA)
Ostelo, R. W. J. G., Deyo, R. A., Stratford, P., Waddell, G., Croft, P., Von Korff, M., Bouter, L. M., & de Vet, H. C.
W. (2008). Interpreting change scores for pain and functional status in low back pain: towards international
consensus regarding minimal important change. Spine, 33(1), 90-94.
https://doi.org/10.1097/BRS.0b013e31815e3a10
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SPINE Volume 33, Number 1, pp 90–94
©2008, Lippincott Williams & Wilkins, Inc.
Interpreting Change Scores for Pain and Functional
Status in Low Back Pain
Towards International Consensus Regarding Minimal
Important Change
Raymond W. J. G. Ostelo, PhD,*† Rick A. Deyo, PhD,‡ P. Stratford, PhD,§
Gordon Waddell, MSc, MD,¶ Peter Croft, PhD,储 Michael Von Korff, PhD,**
Lex M. Bouter, PhD,*†† and Henrica C. de Vet, PhD*
Study Design. Literature review, expert panel, and a
workshop during the “VIII International Forum on Primary
Care Research on Low Back Pain” (Amsterdam, June 2006).
Objective. To develop practical guidance regarding
the minimal important change (MIC) on frequently used
measures of pain and functional status for low back pain.
Summary of Background Data. Empirical studies have
tried to determine meaningful changes for back pain, us-
ing different methodologies. This has led to confusion
about what change is clinically important for commonly
used back pain outcome measures.
Methods. This study covered the Visual Analogue
Scale (0 –100) and the Numerical Rating Scale (0–10) for
pain and for function, the Roland Disability Question-
naire (0–24), the Oswestry Disability Index (0 –100), and
the Quebec Back Pain Disability Questionnaire (0 –100).
The literature was reviewed for empirical evidence. Addi-
tionally, experts and participants of the VIII International
Forum on Primary Care Research on Low Back Pain were
consulted to develop international consensus on clinical
interpretation.
Results. There was wide variation in study design and
the methods used to estimate MICs, and in values found
for MIC, where MIC is the improvement in clinical status
of an individual patient. However, after discussion among
experts and workshop participants a reasonable consen-
sus was achieved. Proposed MIC values are: 15 for the
Visual Analogue Scale, 2 for the Numerical Rating Scale,
5 for the Roland Disability Questionnaire, 10 for the Os-
westry Disability Index, and 20 for the QBDQ. When the
baseline score is taken into account, a 30% improvement
was considered a useful threshold for identifying clinically
meaningful improvement on each of these measures.
Conclusion. For a range of commonly used back pain
outcome measures, a 30% change from baseline may be
considered clinically meaningful improvement when
comparing before and after measures for individual pa-
tients. It is hoped that these proposals facilitate the use of
these measures in clinical practice and the comparability
of future studies. The proposed MIC values are not the
final answer but offer a common starting point for future
research.
Key words: outcome measures, low back pain, mini-
mal important change. Spine 2008;33:90 –94
Patient-reported outcomes are well established and there
are now many self-reported measures used for low back
pain. To facilitate comparison of results between studies
and to enable the pooling of data in systematic reviews,
an international group of investigators recommended a
standardized “core” set of measures in 1998
1
which was
revised in 2000.
2
They suggested 5 domains: pain, back
specific function, work disability,generic health status, and
patient satisfaction.
2
This article focuses on what are argu
-
ably the 2 most fundamental clinical outcomes: pain and
back specific function.
The measurement properties of commonly used mea-
sures (i.e., questionnaires) in these 2 domains are well
established
3,4
but the challenge remains: what consti
-
tutes an important change? Statistical significance does
not necessarily mean the change is clinically important.
5
For some clinical outcomes such as blood pressure, em-
pirical research, and clinical experience may produce a
general feeling whether a change is important or not. But
the importance of changes on many questionnaires is less
intuitively apparent.
6
Several empirical studies have tried to determine im-
portant changes on these questionnaires, using different
methodologies. Some use a distribution-based, whereas
others use an anchor-based approach. Distribution-
based methods express the observed change in a stan-
dardized metric. Examples are the effect size and the
standardized response mean, where the numerators of
both parameters represent the mean change and the de-
nominators are the standard deviation at baseline and
the standard deviation of change, respectively. Another
is the standard error of measurement, which relates the
reliability of the measurement instrument to the standard
deviation of the population.
7
Effect size and standardized
From the *EMGO Institute, VU University Medical Centre; †Institute
for Health Sciences, VU University, Amsterdam, The Netherlands;
‡Department of Medicine, University of Washington, Seattle, WA;
§Department of Clinical Epidemiology and Biostatistics, School of Re-
habilitation Science, McMaster University, Hamilton, Ontario, Can-
ada; ¶UnumProvident Centre for Psychosocial and Disability Re-
search, Cardiff University, Cardiff, UK; 储Primary Care Musculoskeletal
Research Centre, Keele University, UK; **Centre for Health Studies,
Group Health Cooperative, Seattle, WA; and ††Executive Board of VU
University, Amsterdam, The Netherlands.
Acknowledgment date: April 4, 2007. Revision date: April 26, 2007.
Acceptance date: May 10, 2007.
The manuscript submitted does not contain information about medical
device(s)/drug(s).
No funds were received in support of this work. No benefits in any
form have been or will be received from a commercial party related
directly or indirectly to the subject of this manuscript.
Address correspondence and reprint requests to Raymond W.J.G. Os-
telo, PhD, EMGO Institute, VU University Medical Center, Van der
Boechorststraat 7, 1081 BT Amsterdam, The Netherlands; E-mail:
r.ostelo@vumc.nl, www.emgo.nl
90
response mean are relative representations of change
(i.e., without units), whereas standard error of measure-
ment provides a number in the same units as the original
measurement. The major disadvantage of all distribu-
tion-based methods is that they are purely statistical
measures of the magnitude of the change: they do not say
anything about its clinical importance.
Anchor-based methods use some external criterion to
operationalize the importance of the observed change:
i.e., the concept of “minimal importance” is explicitly
defined and incorporated in the method. Many different
anchors have been used: e.g., comparing change with
achieving (or not) predefined treatment goals or with
retrospective global rating of improvement. Another
problem is the definition of “importance”: e.g., some
authors classify “minimal improvement” (or “slightly
better”) on a global rating as “clinically important”
whereas others classify it as or “no important change” or
“stable.” Because anchor-based approaches do not take
account of measurement precision, they do not necessar-
ily imply statistical significance and consequently that
must be calculated separately.
These methodologic problems have led to confusion
about how to interpret change scores and about deciding
what change is clinically important, even though this is
fundamental to using these measures. The aim of this
article is to develop practical guidance: What is the min-
imal change that can be considered important on fre-
quently used questionnaires of pain and functional status
in low back pain? This is partly a matter of empirical
evidence, and partly of developing some international
consensus on its clinical interpretation.
Materials and Methods
The study covered the core set recommendations and most
commonly used measures: for pain, the Numerical Rating Scale
(scoring range 0 –10)
4
and the Visual Analogue Scale (scoring
range 0 –100)
4
; and for function, the Roland Morris Disability
Questionnaire (scoring range 0 –24)
8
and the Oswestry Disabil
-
ity Index (ODI: scoring range 0 –100).
9
We also included the
Quebec Back Pain Disability Questionnaire (scoring range
0–100),
10
as it is frequently used in randomized controlled
trials.
Empirical Evidence. The literature was reviewed for studies
estimating the minimal important change (MIC) for the above
questionnaires. MEDLINE was searched using a combination
of Medical Subject Heading (MeSH) terms “back pain” and
“low back pain”; the specific names of the questionnaires; and
any of the following terms—“responsiveness,” “minimal(ly)
clinically important change,” “minimal(ly) clinically important
difference,” “minimum clinically important difference,” “min-
imum detectable change,” “smallest detectable change” and
“questionnaires.” Studies were included that reported on the
importance of the change scores. The findings were extracted
and tabulated by 2 of the authors (RO, HdV). This overview
table included the study population, study design, method used
to estimate MIC, and cutoff value(s) for the MIC.
The Expert Panel. Experts involved in recommending the
original core set, or in the update on the relevant measures,
were invited. Additionally, authors of recently published rele-
vant papers on the measures at issue were invited. In total, 6 of
8 invitees agreed to participate. Members of the expert panel
were sent the overview table of the empirical evidence and
asked the following questions: (1) Based on this overview, what
is the most appropriate value for the MIC for the included ques-
tionnaires? (2) Is this also your personal opinion? (3) Should the
MIC also be described in percentages from baseline score?
Workshop. A workshop was organized during the “VIII Inter-
national Forum on Primary Care Research on Low Back Pain” in
Amsterdam (June 2006) to get the input from a wider range of low
back pain researchers. Thirty-six participants were presented with
the overview table, but were not given the expert panel answers to
avoid influencing them. Participants were then divided into 5
groups, each of which discussed the above 3 questions and the
conclusions were reported back to a plenary session.
Synthesis of Recommendations. Answers from the expert
panel and the workshop were synthesized (by RO and HdV)
into provisional proposals for MIC values. Members of the
expert panel reviewed the provisional proposals and issues
raised in the workshop discussion, and their comments were
incorporated into the final recommendations.
Results
Empirical Evidence
Three studies on the Visual Analogue Scale, 5 on the
Numerical Rating Scale, 17 on the Roland Disability
Questionnaire, 5 on the ODI, and 4 on the QBDQ were
identified and included. As expected, there was wide
variation in study design and the methods used to esti-
mate MICs. For example, the included studies used dif-
ferent time intervals for the test-retest (ranging from a
1-day interval to a 1-year interval), different external
criteria to define important were used and many different
statistical techniques were used to calculate MIC. Al-
though these methodologic issues are important and
closely connected with the MIC as estimated in each
study, little (or no) theoretical or empirical justification
was provided for the study design, anchor or method
used for estimating MICs in the identified studies. Within
the framework of this consensus procedure we decided
that the main focus should be on the actual values for
MIC, not the methodology. MICs were generally pre-
sented either as an absolute value for change (intended
for use anywhere in the range of the scale) or as values
dependent on initial scores (e.g., as a percentage). Table
1 presents the range of MIC values for each question-
naire based on the empirical evidence.
Expert Panel and Workshop
Both the expert panel and the workshop participants
experienced difficulty in answering the first question
about the most appropriate MIC cutoffs. This was
mainly because of the heterogeneity of the studies, the
disparate results, and the lack of any clear rationale for
integrating them. Nevertheless, discussion led to reason-
91Interpreting Change Scores in Back Pain
•
Ostelo et al
able consensus. On the second question, personal opin-
ions did not deviate significantly from the answers to
question 1. Apparently, personal opinions were already
included in reaching consensus on the empirical evi-
dence. On the third question, some experts and work-
shop participants felt that 1 simple (absolute) value for
MIC for each questionnaire is easier to produce from the
available evidence. Furthermore, such a uniform value is
more likely to be used in clinical practice. Others felt that
was an oversimplification as there is evidence that MIC is
baseline dependent, so initial values should be taken into
account e.g., as percentage improvement from baseline.
It was therefore decided to work toward consensus on
both issues.
The discussions in the expert group and workshop
raised also several other issues. Debate remains about the
meaning and definition of a “clinically important
change.” For example, some participants regarded
“slightly improved” as clinically important whereas oth-
ers considered this within the range of natural fluctua-
tion. The latter reasoned that an “important” improve-
ment should be greater than these (unimportant) natural
fluctuations. Furthermore, patients may easily say that
they are slightly improved just to please their physician
or therapist. Better methodology will not resolve this;
rather, these are clinical judgments that then determine
the methodology used.
There was also debate about whether different MIC
values should be used for acute, subacute, and chronic
low back pain. After discussion it was agreed on that
there is insufficient empirical evidence to set different
MICs for these different types of low back pain, though
that may already be reflected in baseline scores and
would in any event be difficult to operationalize. Table 2
presents the range of MIC values for each questionnaire
after the first expert panel round and the workshop.
Data Synthesis
The final proposals for the MIC values on each measure
are presented in Table 3. During discussion it was sug-
gested that the definition of MIC should be simple and
generalizable to different outcome measures. When base-
line is taken into account, a 30% improvement was con-
sidered a generally useful guide.
Discussion
This is a first attempt to develop recommendations on
MICs for commonly used measures of pain and function
in low back pain, and the findings must be viewed in light
of the methodologic limitations of this study. Firstly, the
search strategy was not optimal, though as the experts
and participants included many leaders in this field it is
unlikely that important articles were missed. Moreover,
the literature review was not the primary purpose of the
exercise but rather the starting point for discussion and
consensus. The included studies were so heterogeneous
that any additional studies would probably have com-
pounded rather than resolved the problem. Second, the
empirical evidence is limited and heterogeneous and
there are no agreed scientific grounds or empirical evi-
dence to determine the optimum method of estimating
the MIC. Therefore, the results are variable and difficult
to integrate. Finally, consensus was constrained by the
experts and participants who contributed, with a partic-
ular focus on primary care. Nevertheless, MIC values
depend not only on empirical evidence but also on clin-
ical interpretation and judgment, so there is a good ar-
gument for combining empirical evidence and consensus
procedures to come to a reasonable and parsimonious
choice of MIC values.
Table 1. Ranges for MIC Values Based on the
Empirical Evidence
Questionnaire
Scoring
Range
Range of MIC
Values
(Absolute)
Range of MIC Values
(% Improvement From
Baseline)
VAS
11–13
0–100 2.0–29.0 points No empirical evidence
NRS
12,14–16
0–10 1.0–4.5 points 30
RDQ
3,10–12,17–28
0–24 2.0–8.6 points* 30
ODI
3,11–13,21
0–100 4.0–15.0 points No empirical evidence
QBPQ
10,14,21
0–100 8.5–32.9 points No empirical evidence
Absolute values presented are intended for use anywhere in the range of the
scale.
*11–13 points for high baseline scores, when these were taken into account.
VAS indicates Visual Analogue Scale; NRS, Numerical Rating Scale; RDQ,
Roland Morris Disability Questionnaire; ODI, Oswestry Disability Index;
QBPQ, Quebec Back Pain Disability Questionnaire.
Table 2. Ranges for MIC Values After First Expert Panel
and Workshop
Questionnaire
Scoring
Range
Range of MIC
Values
(Absolute)
Range of MIC Values
(% Improvement From
Baseline)
VAS 0–100 15.0–20.0 points 20–30
NRS 0–10 1.0–2.0 points 20–30
RDQ 0–24 3.0–6.0 points 20–30
ODI 0–100 10.0–12.0 points 20–30
QBPQ 0–100 20.0 points 20–30
Absolute values presented are intended for use anywhere in the range of the
scale.
VAS indicates Visual Analogue Scale; NRS, Numerical Rating Scale; RDQ,
Roland Morris Disability Questionnaire; ODI, Oswestry Disability Index;
QBPQ, Quebec Back Pain Disability Questionnaire.
Table 3. Proposed Cutoff Values for MIC
Questionnaire
Scoring
Range
MIC
(Absolute Cutoff)
MIC (% Improvement
From Baseline)
VAS 0–100 15 30
NRS 0–10 2 30
RDQ 0–24 5 30
ODI 0–100 10 30
QBPQ 0–100 20 30
Absolute values presented are intended for use anywhere in the range of the
scale.
VAS indicates Visual Analogue Scale; NRS, Numerical Rating Scale; RDQ,
Roland Morris Disability Questionnaire; ODI, Oswestry Disability Index;
QBPQ, Quebec Back Pain Disability Questionnaire.
92 Spine
•
Volume 33
•
Number 1
•
2008
There was debate about whether MICs should be ex-
pressed as a single value or as a range that includes all
reasonable values. Ranges, however, require the user to
know when to use the larger or smaller values. Many
may be tempted to use the smallest MIC in order to
demonstrate more improvement, but that may not be
most appropriate to the patient group or intervention.
There was insufficient empirical evidence to set different
MICs for acute or chronic low back pain, though that
may already be reflected in baseline scores and would in
any event be difficult to operationalize. Nevertheless, dif-
ferent MICs may be more appropriate for different pa-
tients or contexts, e.g., children or surgical patients.
Again, a smaller MIC may be appropriate to a simple,
cheap, and safe intervention, whereas a larger MIC may
be more appropriate to an expensive, risky procedure.
Indeed, an ODI MIC of 15 points has been suggested for
surgical interventions,
3
compared with the 10 points
proposed here (Table 3). Types of patients and treat-
ments were not specifically taken into account in these
proposals. Thus, the proposed values should be taken as
generic lower limits for the MICs which can (and should)
be modified when necessary.
Many participants stressed that the proposed MIC
values were for individual rather than group changes.
Randomized controlled trials typically analyze group
differences between treatment and control interventions,
and investigators and clinicians assume that whether the
difference in the means is less than the MIC, the treat-
ment effect is unimportant. However, it is entirely possi-
ble that individual patients in the trial do show clinically
important improvement.
29
Therefore, Guyatt et al
29
have proposed a method for estimating the proportion of
patients who benefit from a treatment when the outcome
measure is a continuous variable. Recent Food and Drug
Administration Guidance states that there may be situa-
tions where it is more reasonable to look at individual
rather than group responses, provided the definition of re-
sponders is based on prespecified criteria backed by empir-
ical evidence.
30
The MIC values proposed in this study can
be used for labeling individuals as responders to treatment.
It is hoped that these proposals will facilitate the use of
these measures of pain and functional limitation in clinical
practice. The proposed MIC values are not the final answer
but guidance, which may offer a common starting point for
future research. They should also improve the comparabil-
ity of future studies, pooling, and the clinical interpretation
of results. Future research may yield new evidence that ne-
cessitates modification of this guidance.
Key Points
● Empirical studies have tried to determine mean-
ingful changes for back pain, using different meth-
odologies. This has led to confusion about what
change is clinically important for commonly used
back pain outcome measures.
● This article provides practical guidance regarding
the MIC for a range of commonly used back pain
outcome measures for pain and functional status.
● It is hoped that these proposals facilitate the use
of these measures in clinical practice and the com-
parability of future studies. The proposed MIC val-
ues are not the final answer but offer a common
starting point for future research, which may yield
new evidence that necessitates modification of this
guidance.
Acknowledgments
The authors gratefully acknowledge the contribution of
all who participated in this workshop during Low Back
Pain Forum VIII, June 2006, in Amsterdam, the Nether-
lands.
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