Psychometric measurement of PEI in chronic musculoskeletal pain
score was related to a positive change in complaints
compared with baseline. Haughney et al. (5) found a
fair correlation (0.30) between higher enablement and
improvement in asthma-related quality of life after
treatment. Ožvačić Adžić et al. (31) found an associa-
tion between low enablement and poor self-perceived
health in patients consulting a GP. These results suggest
that a higher PEI score may be related both to better
current health and improvement in health over time.
Self-rated change
The SRC of a measure depends on several factors,
such as the patient group being studied and the method
used to calculate the measure (27). In this study the
SRC in perceived enablement for the WAD, CR and
MixCP groups were 5, 6 and 4, respectively, illustrating
that the SRC may be different for different groups. In
patients in primary care, a PEI score ≥ 6 was reported
to indicate clinically meaningful “enablement” (32).
However, this was an arbitrary judgement by the ori-
ginal authors (3).
Although overall model quality was acceptable;
for example, in the model with all participants ap-
proximately one-third were misclassified. The GPE,
a more generic measure of health effects, correlated
moderately with the PEI, justifying its use as an anchor.
Furthermore, the PEI was correlated with change in
health and disability measures, as well as with the
GPE. The PEI had high sensitivity and specificity, but
low PPV. As the PPV depends on prevalence this may
partly have stemmed from a low proportion of patients
who improved (23.6%, n = 119) compared with those
who did not (76.4%, n = 385). In summary, we suggest
a study-specific self-rated important change should be
applied. Since it may not be realistic to determine the
cut-off for every new population, a score of at least 4
on the PEI is recommended for important self-rated
change in perceived enablement in patients with chro-
nic pain. However, due to participant misclassification
the instrument must be administered with caution as it
may be overly sensitive.
Strengths and weaknesses
The relatively large number of patients included from
different healthcare centres, with different chronic
musculoskeletal conditions, and treated with different
interventions, is a strength of this study, as this might
enhance the generalizability of the results. It is also a
strength to have a relatively large number of patients
in the context of the planned statistical analyses.
In the WAD and MixCP groups the proportion of
women was high, making the results less generalizable
to men. In the MixCP group a considerable number
of patients did not complete the self-reported ques-
595
tionnaire after the treatment period. One reason for
this was that a number of patients never finished the
treatment, either because they stopped participating
in treatment or because the rehabilitation team found
a different treatment to be more appropriate. Another
reason for this was administrative issues, since the
staff was not very experienced in administration of
the questionnaires. There were only a few differences
between those who did vs did not complete the ques-
tionnaires, which might indicate that there was no
significant selection bias. However, a better response
rate would be preferable.
The PEI measures change in enablement, which
might be considered a limitation or weakness of the
instrument. Patients with less experience and know-
ledge of their disease might be more likely to improve
in enablement (i.e. to have higher PEI scores) than
patients who have experienced problems for a longer
period of time. In addition, patients might be satisfied
with their treatment even if there was no improvement
in enablement (13). Another issue is that, since the PEI
measures change in enablement, it is not known how
“enabled” the patient actually is. Traditionally, the
measurement of, for example, the minimal important
change is based on the difference between 2 measure-
ments. It is important to mention that in this study the
self-rated change is based on 1 measurement with the
PEI. It is considered important to investigate respon-
siveness as a measurement property. Responsiveness
is defined as “the ability of an instrument to detect
change over time in the construct to be measured.”
However, the PEI is aimed to measure self-rated
change; therefore, assessment of responsiveness was
judged not to be appropriate. Further development of
the instrument measuring current patient enablement
at different time-points might improve the possibility
to measure responsiveness. For this, it would also be
better to use response options with a larger range (e.g.
0–10) instead of the current limited response options
0–2, leaving little room for change.
A recent publication (33) recommends 10 criteria
for evaluating the content validity of patient-reported
outcome measures, asking about the relevance, com-
prehensiveness and comprehensibility of the items,
response options, and instructions. This paper investi-
gated only parts of these criteria. The PEI was not
originally developed for use in patients with chronic
musculoskeletal pain, and further assessment of the
content validity is recommended (27, 33).
In conclusion, the PEI showed fair content validity,
construct validity, and internal consistency in indi-
vidual patients with chronic musculoskeletal pain.
The estimated SRC values could be used to indicate
relevant changes in patient enablement in clinical
practice and to guide interpretation of the results of
J Rehabil Med 51, 2019