P. Enthoven et al.
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Fig. 1. Receiver operating characteristic (ROC) curve for different cut-off points for the Patient Enablement Instrument (PEI) in different groups.
(a) All participants, n = 504, area under the curve (AUC) 0.897 (95% confidence interval (95%CI) 0.867–0.928). (b) Whiplash-associated disorders
(WAD) group (n = 116), AUC 0.914 (CI 0.858–0.970). (c) Cervical radiculopathy (CR) group, n = 112, AUC 0.862 (CI 0.794–0.929). (d) Mixed
chronic pain (MixCP) group, n = 276, AUC 0.914 (CI 0.858–0.970).
small (< 0.10, with 2 exceptions that were close to
0.10) (24). This supports the internal construct vali-
dity of the PEI. The original authors investigated the
construct validity by adding 3 items to the instrument
and found the construct validity of the original 6 items
to be satisfactory (3). To our knowledge, only 1 study,
conducted in Japanese patients with chronic illnesses,
found that the PEI consisted of 2 principal factors
(6). The first factor comprised questions 1–4, and the
second factor comprised questions 5 and 6. However,
other studies using factor analysis support the finding
that the PEI is unidimensional (10, 11).
Internal consistency of the Patient Enablement
Instrument
Cronbach’s alpha coefficient for the PEI varied bet-
ween 0.878 and 0.907, indicating good internal con-
sistency (27). For the original PEI, Cronbach’s alpha
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coefficient was 0.925, and it decreased each time an
item from 2 different satisfaction scales was added or
when any of the 6 PEI items was removed. This sug-
gests that the 6 original PEI items comprise a unified
group of questions that differ from other concepts, such
as patient satisfaction (3, 4). Other studies conducted in
primary care found Cronbach’s alpha values between
0.86 and 0.93 (2, 6, 10, 19), while studies with a PEI
that was modified to fit patients with asthma reported
values between 0.87 and 0.92 (5, 11), all within sug-
gested alpha limits (27).
Relationship between the Patient Enablement
Instrument and other measures
As hypothesized, higher PEI score showed a fair to
moderate relationship with better function and men-
tal and general health in all groups with chronic pain
after treatment (Table VI). Furthermore, a higher PEI