physical therapy assisgment

Physical Functioning Before and After
Total Hip Arthroplasty:
Perception and Performance
Inge van den Akker-Scheek, Wiebren Zijlstra, Johan W Groothoff, Sjoerd K Bulstra,
Martin Stevens

Background and Purpose. Self-report and performance-based measures of
physical functioning in people before and after total hip arthroplasty seem to present
different information. The relationship between these different measures is not well
understood, and little information is available about changes in this relationship over
time. The aims of this study were: (1) to determine the relationship between
self-report and performance-based measures of physical functioning before and after
total hip arthroplasty, (2) to assess the influence of pain on the relationship, and (3) to
determine whether the relationship changes over time.

Subjects and Methods. Seventy-five subjects admitted for total hip arthro-
plasty were included and examined before and 6 and 26 weeks after surgery. The
relationships between the Western Ontario and McMaster Universities Osteoarthritis
Index (WOMAC) physical functioning subscale and walking speed and gait variability
were examined by use of generalized estimating equations, which included interac-
tions with time and the WOMAC pain subscale.

Results. The relationship between self-report and performance-based measures of
physical functioning was poor. Pain appeared to have a considerable influence on
self-reported physical functioning. The relationship did not appear to change over
time.

Discussion and Conclusion. The influence of pain on self-reported physical
functioning serves as an explanation for the poor relationship between self-reported
and performance-based physical functioning. When using a self-report measure such
as the WOMAC, one should realize that it does not seem to assess the separate
constructs—physical functioning and pain—that are claimed to be measured.

I van den Akker-Scheek, PhD, is
Human Movement Scientist and
Epidemiologist, Department of
Orthopedics, University Medical
Center Groningen, University of
Groningen, PO Box 30001, 9700
RB Groningen, the Netherlands.
Address all correspondence to
Dr van den Akker-Scheek at:
[email protected]

W Zijlstra, PhD, is Human Move-
ment Scientist, Center for Human
Movement Sciences, University
Medical Center Groningen, Uni-
versity of Groningen.

JW Groothoff, PhD, is Professor of
Work and Health, Department of
Health Sciences, University Medi-
cal Center Groningen, University
of Groningen.

SK Bulstra, MD, PhD, is Orthope-
dic Surgeon, Professor of Ortho-
pedics, and Head of Department,
Department of Orthopedics, Uni-
versity Medical Center Groningen,
University of Groningen.

M Stevens, PhD, is Research Co-
ordinator and Human Movement
Scientist, Department of Ortho-
pedics, University Medical Cen-
ter Groningen, University of
Groningen.

[van den Akker-Scheek I, Zijlstra
W, Groothoff JW, et al. Physical
functioning before and after total
hip arthroplasty: perception and
performance. Phys Ther. 2008;88:
712–719.]

© 2008 American Physical Therapy
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Outcomes after total hip arth-roplasty can be assessed bymeans of self-report mea-
sures; the Western Ontario and Mc-
Master Universities Osteoarthritis In-
dex (WOMAC) is a disease-specific
questionnaire and is one of the
most widely used and recommended
measures.1,2 The questionnaire is
completed by the patient; the score
provides an indication of the pa-
tient’s physical functioning, stiffness,
and pain. Besides self-report mea-
sures, performance-based measures,
in which the patient actually has to
perform one or more activities of
daily living, are available. Advantages
and disadvantages have been re-
ported for both kinds of measures.3,4

The advantages of self-report mea-
sures are that they are easy to ad-
minister, are inexpensive, and can
evaluate multiple aspects of func-
tion in one test. Mentioned disad-
vantages are that self-report mea-
sures are influenced by expectations
and beliefs of the patients and by
impaired cognition and errors in
memory; performance-based instru-
ments do not have these disadvan-
tages. However, the disadvantage of
performance-based instruments is
that activities often have to be as-
sessed in an artificial laboratory en-
vironment, a task that can be time-
consuming and expensive. With the
introduction of ambulation measur-
ing devices that use body-fixed sen-
sors, physical functioning can be as-
sessed objectively without these
disadvantages.5 Spatiotemporal gait
parameters, such as walking speed,
can be accurately determined, and
step-to-step variability as a measure
of gait efficiency can be calculated
from the obtained measurements.

Research into the relationship be-
tween self-report and performance-
based measures has shown a poor
to moderate relationship between
these 2 types of measures.3,6,7 Each
measure seems to assess different
aspects of recovery. It is recom-

mended, therefore, that both mea-
sures be used to obtain full insight
into outcomes after total hip arthro-
plasty because these measures are
considered to be complementary.3,8

However, research into the possible
explanations for the poor to moder-
ate relationship is scarce. Recently,
Terwee et al9 investigated the influ-
ence of pain on the relationship be-
tween self-report and performance-
based outcome measures before and
after total knee arthroplasty. They
discovered that self-report measures
of physical functioning are influenced
by pain more than are performance-
based measures, a finding that could
explain the low correlation between
them. It is our hypothesis that this ex-
planation also is valid for total hip
arthroplasty.

Additionally, most research determin-
ing the relationship between self-
report and performance-based mea-
sures is limited to measurement at one
point in time (eg, before surgery or 12
months after surgery). Therefore, in-
formation about whether the relation-
ship between these 2 types of mea-
sures changes over time is scarce.
Research is needed on the relationship
between self-report and performance-
based measures in people before total
hip arthroplasty as well as across the
spectrum of recovery after surgery.3,10

Research on total knee arthroplasty
demonstrated that the correlations be-
tween the self-report and performance-
based measure scores changed over
time after surgery; the correlations
were somewhat better 3, 6, and 12
months after surgery than they were
before surgery.9 This change in cor-
relations over time can be explained
by the influence of reduced pain. Be-
fore surgery, patients are in pain,
which is hypothesized to influence
the self-report measure; because of
the pain, patients value their physi-
cal functioning less than is actually
the case. There is an expectation
that pain will decrease markedly
shortly after surgery, and it is hy-

pothesized that this sudden change
will influence self-reported physical
functioning: Patients overrate their
physical functioning compared with
what the performance-based mea-
sure shows because they suddenly
do not perceive any pain while exe-
cuting the activities. Over the long
term after surgery, better concor-
dance between self-reported and
performance-based physical func-
tioning is expected because patients
do not perceive pain over time and,
therefore, can provide a more accu-
rate evaluation of their physical func-
tioning. We hypothesize, therefore,
that in patients with total hip arthro-
plasty, the relationship between self-
report and performance-based out-
come measures will change over
time, as will the influence of pain.

The aims of this study were: (1) to
determine the relationship between
self-report and performance-based
measures of physical functioning
after total hip arthroplasty, (2) to
assess the influence of pain on the
relationship, and (3) to determine
whether the relationship changes
over time. In this study, the
WOMAC physical functioning sub-
scale (WOMAC-PF) was used as the
self-report outcome measure and
walking speed and step-to-step vari-
ability were used as the performance-
based outcome measures in people
before total hip arthroplasty and
over the short term and long term
after surgery.

Method
Subjects
People admitted to a medical center
orthopedic department for unilateral
total hip arthroplasty and participat-
ing in the short-stay program be-
tween September 2002 and August
2004 were included in the study.
The criteria for the short-stay pro-
gram were as follows: estimated sur-
gery time of less than 120 minutes,
weight of less than 110 kg, estimated
hospital stay of less than 6 days, no

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signs of severe mobility disablement
or psychological dysfunction, and no
severe deformity of the spine. Study
participants were allowed to start
walking with aids on the first day
after surgery and were discharged on
day 5 after surgery unless there were
complications.

In total, 87 people were admitted for
total hip arthroplasty during the
study period. All were willing to par-
ticipate in the study. Measurements
were performed at the time of admis-
sion and 6 and 26 weeks after the
surgery, when the study participants
visited the outpatient clinic. The par-
ticipants were asked to complete the
WOMAC, and gait analysis was per-
formed. Data on participant charac-
teristics such as sex, age, and body
mass index (BMI) were gathered at
admission.

Of the 87 people willing to partici-
pate in the study, 12 were excluded
from further analyses because they
did not complete the questionnaire
or the gait analysis at all 3 measure-
ment times for various reasons: 1
had severe surgical complications, 1
moved out of the country, 1 died, 2
had health problems attributable to
causes unrelated to the orthopedic
surgery, 2 refused further participa-
tion because of personal circum-
stances, 4 did not visit the outpatient
clinic, and 1 had a total hip arthro-
plasty on the contralateral side. The
remaining 75 participants were pre-
dominantly women (n�53, 70.7%),
with a mean age of 62.7 years
(SD�11.7) and a mean BMI of 26.6
kg�m�2 (SD�3.4). The mean length
of the hospital stay was 7.0 days
(SD�3.3).

Measures
The Dutch version of the WOMAC
was used; it has been proven valid
and reliable for people before and
after total hip arthroplasty.11,12 The
WOMAC is a disease-specific, self-
report outcome measure for people

before and after hip arthroplasty and
consists of the subscales physical
functioning, stiffness, and pain. Two
of the subscales, the WOMAC-PF (17
items) and the WOMAC pain sub-
scale (WOMAC-P) (5 items), were
used in this study. Responses were
given on a 5-point Likert scale.
Scores from both subscales were re-
coded into a 100-point scale, with a
higher score representing better
physical functioning or less pain.

Gait analysis was performed with
the DynaPort System.* This is an am-
bulation system consisting of a data
recorder (dimensions�125�95�34
mm; weight�295 g) that is attached
to an individual’s lower back with
a neoprene belt around the waist,
over the individual’s clothes. The
data recorder contains 3 uniaxial,
piezoelectricity-resistive accelerome-
ters that measure acceleration in the
frontal, sagittal, and transverse planes
and a memory card on which data
are stored. Three penlight batteries
are attached to the belt. In this study,
participants were asked to walk
20 m at their preferred speed in a
hospital corridor. After each mea-
surement, the data were transferred
from the memory card to a personal
computer and displayed graphically.
The beginning and end of each test
part were marked manually in the
DynaPort software. Analysis of the
accelerometer signals and extraction
of data for the gait parameters were
performed by McRoberts BV.* Sev-
eral movement features can be deter-
mined from the accelerometer sig-
nals.13–15 Only the parameters of
walking speed and step-to-step vari-
ability were used in this study as
measures of gait steadiness because
they reliably reflect changes in an
individual’s gait efficiency.16 Step-to-
step variability is expressed as the
coefficient of variation (CV), as fol-
lows: (SD of step duration/mean

step duration)�100. The ambulation
method is used to determine spatio-
temporal gait parameters from
lower-trunk accelerations. In previ-
ous studies,13–15 this method was
proven to be a valid means for deter-
mining gait parameters.

Data Analysis
Descriptive statistics (mean and SD)
were used to describe participant
characteristics, scores on the
WOMAC-PF and the WOMAC-P, pre-
ferred walking speed, and step-to-
step variability (expressed as the
CV) at the 3 measurement times
(before surgery and 6 weeks and 6
months after surgery). General linear
model repeated-measures analyses
were used to determine whether the
scores changed over time. General
linear model repeated-contrast anal-
yses were used to determine whether
the scores changed between the
measurements obtained before sur-
gery and over the short term after
surgery or between the measure-
ments obtained over the short term
and over the long term after surgery,
or both. Pearson correlation coeffi-
cients were calculated for the scores
obtained before surgery (Tab. 1).

The relationship between the
WOMAC-PF and preferred walking
speed was assessed by applying gen-
eralized estimating equations (GEEs)
to longitudinal data to account for
correlations between repeated ob-
servations for each subject. First, a
“naive” linear regression analysis is
carried out, and regression coeffi-
cients are estimated, assuming that
the repeated observations within
one subject are independent.17 Be-
cause this is not the case, a correc-
tion must be made for these within-
subject correlations. This is done by
adding to the regression model a cor-
relation matrix that consists of an
estimation of the correlations be-
tween the different time points
within a subject. In this study, an
exchangeable correlation structure

* McRoberts BV, Raamweg 43, 2596 HN, The
Hague, the Netherlands.

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was used, assuming all correlations
to be the same. The regression coef-
ficients are then reestimated, with
correction for the dependency of the
observations. Through standardiza-
tion of the regression coefficients
[(regression coefficient�SDx)/SDy],
the coefficients can be interpreted as
correlation coefficients.

In the first GEE model, the WOMAC-
PF score was included as a depen-
dent variable and preferred walking
speed was included as an indepen-
dent variable. In the second model,
the WOMAC-P score was added. Ad-
ditionally, a walking speed�time in-
teraction and a pain�time interac-
tion were included (models 3 and 4).
The participant characteristics of
sex, age, and BMI were included as
potential confounders (model 5).
The regression coefficients were
standardized. The complete analysis
was repeated with the CV [(SD of
step duration/mean step dura-
tion)�100] instead of preferred
walking speed as an independent
variable.

The Statistical Package for the Social
Sciences, version 14.0,† and STATA,

version 9.1,‡ were used for data anal-
ysis. A P value of less than .05 was
considered statistically significant.

Results
The mean WOMAC-PF and WOMAC-
P scores, preferred walking speed,
and CV at the 3 assessment times are
shown in Table 2. For all variables, a
significant improvement was seen
over the 3 measurement times (over-
all time effect; P�.001). For the
WOMAC-PF, a significant improve-
ment was seen between each of the
3 measurement times. The overall
significant improvement seen for

the WOMAC-P and CV was attribut-
able to a significant improvement be-
tween the measurements before sur-
gery and over the short term after
surgery. For walking speed, the over-
all significant improvement was at-
tributable to a significant improve-
ment between the 2 measurements
after surgery.

The results of the GEE analysis with
WOMAC-PF as the dependent vari-
able and preferred walking speed as
the independent variable are shown
in Table 3. In model 1, the standard-
ized regression coefficient of pre-
ferred walking speed was .40; adding
WOMAC-P to the regression model

† SPSS Inc, 233 S Wacker Dr, Chicago, IL
60606.

‡ StataCorp LP, 4905 Lakeway Dr, College Sta-
tion, TX 77845.

Table 1.
Pearson Correlation Coefficients for the Measures Before Surgerya

Measure Correlation With:

WOMAC-PF PWS CV WOMAC-P

WOMAC-PF 1.00

PWS .13 1.00

CV .13 �.28b 1.00

WOMAC-P .68c �.07 .30b 1.00

a WOMAC�Western Ontario and McMaster Universities Osteoarthritis Index, PF�physical functioning
subscale of the WOMAC, PWS�preferred walking speed, CV�coefficient of variation, P�pain subscale
of the WOMAC.
b P�.05.
c P�.01.

Table 2.
Mean (SD) of the Self-report and Performance-based Outcome Measures and Pain at the 3 Measurement Times and Results of
the General Linear Model Repeated-Measures Analysisa

Measure X (SD) P for: Partial
eta
Squared

Before
Surgery

Short Term
After
Surgery

Long Term
After
Surgery

Overall
Time
Effect

Before Surgery
vs Short Term
After Surgery

Short Term
After Surgery
vs Long Term
After Surgery

WOMAC-PF
score

46.9 (16.5) 72.8 (17.2) 78.4 (14.9) <.001 <.001 .002 .65 PWS (m/s)b 0.93 (0.20) 0.94 (0.19) 1.12 (0.20) <.001 .602 <.001 .44 CV (%)b 12.4 (6.1) 10.1 (3.6) 9.9 (3.2) .001 .007 .267 .11 WOMAC-P score 50.4 (19.0) 84.1 (14.4) 84.9 (16.7) <.001 <.001 .707 .67 a Preferred walking speed (PWS) and coefficient of variation (CV) before surgery were calculated for 69 participants because 6 measurements were missing as a result of technical problems. Significant values are shown in boldface type. WOMAC�Western Ontario and McMaster Universities Osteoarthritis Index, PF�physical functioning subscale of the WOMAC, P�pain subscale of the WOMAC. b Normative data (n�19, comparable characteristics)5: PWS�1.32 m/s (SD�0.15 m/s), CV�8.1% (SD�3.2%). Hip Arthroplasty and Physical Functioning June 2008 Volume 88 Number 6 Physical Therapy f 715 D ow nloaded from https://academ ic.oup.com /ptj/article/88/6/712/2742310 by A P TA M em ber A ccess user on 30 M ay 2021 resulted in a decrease to .22 (model 2). Neither the interaction term pre- ferred walking speed�time (model 3) nor the interaction term WOMAC- P�time (model 4) was significant; this result implies that the contribu- tions of preferred walking speed and pain to the regression model do not change over time. On the basis of the fact that the regression coefficient of PWS showed only a minimal change when the participant characteristics of sex, age, and BMI were added to the regression model (.21 versus .22), these characteristics are not considered to be confounders (model 5). Table 4 shows the results of the GEE analysis with WOMAC-PF as the de- pendent variable and CV as the inde- pendent variable. In model 1, the standardized regression coefficient Table 3. Results of the Generalized Estimating Equation (GEE) Analysis With Physical Functioninga as the Dependent Variable and Preferred Walking Speed (PWS) as the Independent Variableb GEE Model Independent Variable Standardized Regression Coefficient (95% Confidence Interval) 1. PWS PWS .40 (.29 to .51) 2. PWS�WOMAC-P PWS .22 (.14 to .29) WOMAC-P .77 (.69 to .85) 3. PWS�WOMAC-P �Time�PWS� time interaction PWS .16 (�.01 to .32) WOMAC-P .66 (.55 to .77) Interaction NS 4. PWS�WOMAC-P �Time�WOMAC-P �time interaction PWS .19 (.10 to .29) WOMAC-P .66 (.49 to .83) Interaction NS 5. PWS�WOMAC-P �Participant characteristics (BMI, age, sex) PWS .21 (.12 to .30) WOMAC-P .77 (.69 to .85) a From the physical functioning subscale of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). b P�WOMAC pain subscale score, NS�not significant, BMI�body mass index. Table 4. Results of the Generalized Estimating Equation (GEE) Analysis With Physical Functioninga as the Dependent Variable and Coefficient of Variation (CV) as the Independent Variableb GEE Model Independent Variable Standardized Regression Coefficient (95% Confidence Interval) 1. CV CV �.14 (�.26 to �.03) 2. CV�WOMAC-P CV �.11 (�.18 to �.03) WOMAC-P .82 (.74 to .89) 3. CV�WOMAC-P �Time�CV� time interaction CV �.07 (�.16 to .02) WOMAC-P .70 (.59 to .80) Interaction NS 4. CV�WOMAC-P �Time�WOMAC-P �time interaction CV �.08 (�.16 to .00) WOMAC-P .68 (.52 to .85) Interaction NS 5. CV�WOMAC-P �Participant characteristics (BMI, age, sex) CV �.09 (�.17 to �.01) WOMAC-P .82 (.74 to .89) a From the physical functioning subscale of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). b P�WOMAC pain subscale score, NS�not significant, BMI�body mass index. Hip Arthroplasty and Physical Functioning 716 f Physical Therapy Volume 88 Number 6 June 2008 D ow nloaded from https://academ ic.oup.com /ptj/article/88/6/712/2742310 by A P TA M em ber A ccess user on 30 M ay 2021 of CV was �.14; adding WOMAC-P to the regression model resulted in a decrease to �.11, but there was an overlap of the 95% confidence inter- vals (model 2). As in the models with PWS as the independent variable, neither the interaction term CV� time (model 3) nor the interaction term WOMAC-P�time (model 4) was significant. The regression coef- ficient of CV showed only a minimal change when the participant charac- teristics of sex, age, and BMI were added to the regression model (�.11 versus �.09); therefore, these char- acteristics are not considered to be confounders (model 5). Discussion The aims of the present study were to determine the relationship be- tween self-report (WOMAC-PF) and performance-based (walking speed and step-to-step variability) out- come measures of physical function- ing in people with total hip arthro- plasty, to assess the influence of pain on the relationship, and to de- termine whether the relationship changes over time. Pain and a deterioration in physical functioning are the primary reasons for a total hip arthroplasty. In the early period after surgery, pain is re- duced, although physical function- ing may be diminished compared with that before surgery because pa- tients have just undergone surgery and usually walk with crutches in the first few weeks after surgery.16 However, the measurements that we obtained in the short term after surgery already indicated an im- provement in the self-reported phys- ical functioning outcome measure (WOMAC-PF). The performance- based measure CV also showed an improvement, but this value could be distorted by the use of crutches by most of the participants at this measurement time. The performance- based measure preferred walking speed, however, did not show an improvement at the 6-week measure- ment time over the value obtained before surgery. This difference in outcomes between a self-report mea- sure and a performance-based mea- sure of the same construct (physical functioning) is consistent with the findings of other investigators.9,18 –20 These observations indicate a poor relationship between self-report and performance-based physical func- tioning measures. The results of the GEE analyses per- formed on our results confirmed that conclusion: The regression coefficient in the model containing WOMAC-PF as a dependent variable and preferred walking speed as an independent vari- able, both measured 3 times, was only .40, and the regression coefficient in the model containing CV as an independent variable was even lower (�.14). The poorer relationship be- tween CV and the WOMAC than be- tween walking speed and the WOMAC was also found by Lindemann et al.16 Our findings are thus in accordance with our hypothesis of a poor rela- tionship between self-report and performance-based measures of phys- ical functioning. Determining the rela- tionship with multiple assessments over time, with correction for the de- pendency of longitudinal data as we applied in our analyses, did not result in adverse findings compared with those of other investigators using cor- relation coefficients. In order to examine the second aim of our study—to determine the influ- ence of pain on the relationship— WOMAC-P was added to the models containing the self-report measure as a dependent variable and the performance-based measure as an in- dependent variable. This method re- sulted in an even lower regression coefficient for preferred walking speed, whereas pain made a great contribution (.77). For the other performance-based measure, CV, the influence of pain was less pro- found; the regression coefficient for CV was slightly lower, but there was an overlap of the 95% confidence intervals. However, for pain there was an equally high regression coef- ficient (.82) in the model containing CV as an independent variable and in the model containing preferred walking speed as an independent variable. Adding participant charac- teristics (age, sex, and BMI) did not change the relationship between the self-report and performance-based measures. The WOMAC-P and the WOMAC-PF appeared to be closely linked. With the WOMAC-PF, pain— or diminishing pain after surgery— also is measured when the aim is to assess solely physical functioning. People seem to be unable to sepa- rate pain and physical functioning when pain is present or when a change in pain has occurred. Through differentiation with 3 subscales, the WOMAC is claimed to measure dif- ferent constructs. However, our re- sults and those of other investiga- tors9,20 question the factorial validity of the WOMAC-PF. The fact that pain was determined with the same questionnaires as those used to assess self-reported physical functioning can be consid- ered a limitation of the present study. Because the present study was part of a larger study,21 we also had access to data from the Medical Out- comes Study 36-Item Health Survey Questionnaire (SF-36). We chose to initially use the WOMAC-P because the WOMAC is a disease-specific questionnaire and the SF-36 is a ge- neric quality-of-life questionnaire. The WOMAC asks about difficulties with specific activities that are prob- lematic for people with arthritis, whereas the SF-36 assesses overall health. Moreover, the WOMAC has been found to be more responsive than the SF-36.18,22 However, when the SF-36 pain subscale was used in- stead of the WOMAC-P, the regres- sion coefficient was somewhat Hip Arthroplasty and Physical Functioning June 2008 Volume 88 Number 6 Physical Therapy f 717 D ow nloaded from https://academ ic.oup.com /ptj/article/88/6/712/2742310 by A P TA M em ber A ccess user on 30 M ay 2021 lower, albeit still high (preferred walking scale model: .77 with WOMAC-P and .64 with SF-36 pain subscale; CV model: .82 with WOMAC- P and .70 with SF-36 pain subscale). This finding strengthens our conclu- sion that pain has a significant influ- ence on the self-report physical func- tioning outcome measure. The third aim of the present study was to determine whether the rela- tionship between self-report and performance-based outcome mea- sures changes over time. On the ba- sis of the observation that the WOMAC-PF scores and the walking speed values developed in different directions over time, we hypothe- sized that the relationship between them would change over time. The interaction term was not significant; this finding implies that the associa- tion did not change over time (Tab. 3). Even when pain was not included in the regression model, the interac- tion term was not significant (data not shown). In the model with CV as an independent variable, the interac- tion term was not significant either (Tab. 4). Lindemann et al16 found similar results; they performed a gait analysis and assessed the WOMAC in people before and after total hip ar- throplasty and did not find changes in correlation coefficients after sur- gery compared with before surgery. Unfortunately, their study had the limitation of a small study group (N�17) and only one measurement after surgery (3 months after surgery). Other investigators did find a chang- ing association. Terwee et al9 found changes in correlation coefficients over time between the DynaPort System knee score (performance- based functioning score) and the WOMAC for people before and af- ter total knee arthroplasty. However, all mentioned studies used correla- tion coefficients to describe the as- sociation between self-reported and performance-based physical function- ing. This method neglects the fact that the observations are repeated measures. With a longitudinal design like that used in the present study, a correction is made …

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You have to be 100% sure of the quality of your product to give a money-back guarantee. This describes us perfectly. Make sure that this guarantee is totally transparent.

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Zero-plagiarism guarantee

The Product ordered is guaranteed to be original. Orders are checked by the most advanced anti-plagiarism software in the market to assure that the Product is 100% original. The Company has a zero tolerance policy for plagiarism.

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Free-revision policy

The Free Revision policy is a courtesy service that the Company provides to help ensure Customer’s total satisfaction with the completed Order. To receive free revision the Company requires that the Customer provide the request within fourteen (14) days from the first completion date and within a period of thirty (30) days for dissertations.

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Privacy policy

The Company is committed to protect the privacy of the Customer and it will never resell or share any of Customer’s personal information, including credit card data, with any third party. All the online transactions are processed through the secure and reliable online payment systems.

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Fair-cooperation guarantee

By placing an order with us, you agree to the service we provide. We will endear to do all that it takes to deliver a comprehensive paper as per your requirements. We also count on your cooperation to ensure that we deliver on this mandate.

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Calculate the price of your order

550 words
We'll send you the first draft for approval by September 11, 2018 at 10:52 AM
Total price:
$26
The price is based on these factors:
Academic level
Number of pages
Urgency

Order your paper today and save 15% with the discount code HAPPY

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Feel free to ask questions, clarifications, or discounts available when placing an order.