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Physiotherapy 97 (2011) 132–138
Inter-rater reliability study of the modified Oxford Grading Scale and the
Peritron manometer
Cristine Homsi Jorge Ferreiraa,∗, Patrícia Brentegani Barbosaa, Flaviane de Oliveira Souza a,
Flávia Ignácio Antônio a, Maíra Menezes Franco a, Kari Bø b
aFaculty of Medicine of Ribeirão Preto, Department of Biomechanics, Medicine and Rehabilitation of Locomotor System, Course of Physiotherapy,
University of São Paulo, Av. Bandeirantes, 3900, Monte Alegre, 14049-900, Ribeirão Preto, SP, Brazil
bNorwegian School of Sport Sciences, Department of Sports Medicine, Oslo, Norway
Abstract
Objective To evaluate the inter-rater reliability of the modified Oxford Grading Scale and the Peritron manometer.
Design All participants were evaluated twice, first by one examiner and 30 days later by a second examiner. Measurements of vaginal squeeze
pressure were compared with the results from the palpation test.
Participants Nineteen women with a mean age of 23.7 years (range 21 to 28 years).
Results Inter-rater reliability for vaginal palpation was fair (κ=0.33, 95% confidence interval 0.09 to 0.57). Using the Peritron manometer,
the difference between examiners was less than 10cmH2O in 11 of the 19 (58%) cases. The palpation test did not differentiate between
weak, moderate, good and strong muscle contractions. This study found fair inter-rater reliability for the modified Oxford Grading Scale and
moderate inter-rater reliability for the Peritron manometer.
Conclusions The inter-rater reliability of vaginal squeeze pressure measurement using the Peritron manometer is acceptable and can be used
in re-evaluations performed by different examiners in clinical practice. However, for research purposes, the ideal situation would be for a
single examiner to assess and re-assess the subject. Vaginal palpation is important in the clinical assessment of correctness of a pelvic floor
muscle contraction, but this study does not support the use of the modified Oxford Grading Scale as a reliable and valid method to measure
and differentiate pelvic floor muscle strength.
© 2010 Chartered Society of Physiotherapy. Published by Elsevier Ltd. All rights reserved.
Keywords: Assessment; Inter-rater reliability; Palpation; Pelvic floor; Squeeze pressure; Strength
Introduction
There is Level 1 evidence that pelvic floor muscle train-
ing is effective for the treatment of mixed and stress urinary
incontinence [1,2]. When conducting pelvic floor muscle
training programmes, it is essential to measure their func-
tion and strength development [3]. Several vaginal palpation
rating scales have been used in clinical practice [3], but the
most commonly used tool in physical therapy seems to be the
modified Oxford Grading Scale [4,5].
Whether a measurement tool should be used in clinical
practice or in research depends on its reliability [6]. Intra-
∗Corresponding author. Tel.: +55 16 36023058; fax: +55 16 36024413.
E-mail address: cristine@fmrp.usp.br (C.H.J. Ferreira).
rater reliability refers to one researcher measuring the same
procedure in the same subject twice, while inter-rater reliabil-
ity refers to two or more clinicians or researchers conducting
measurements of the same subject [6]. Some studies have
reported high intra-rater reliability for vaginal digital assess-
ment [7–9], but inter-rater reliability varies between studies
[10–12]. Although the modified Oxford Grading Scale is con-
sidered by some to be an easy test and well tolerated by
patients [8], others question its use for scientific purposes [9].
Recently, Slieker-ten Hove et al. [13] introduced a new digital
assessment scale based on definitions of outcome measures
of existing scales according to the standardised terminology
of the International Continence Society, showing satisfac-
tory face validity and intra-rater reliability but low inter-rater
reliability.
0031-9406/$ – see front matter © 2010 Chartered Society of Physiotherapy. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.physio.2010.06.007
C.H.J. Ferreira et al. / Physiotherapy 97 (2011) 132–138 133
Pelvic floor muscle strength can be measured with a
manometer or a dynamometer. However, since dynamome-
ters are not commercially available [3,14], strength is
commonly measured by digital muscle testing and manome-
ters [15–18]. The Peritron manometer (Cardio-Design,
Victoria) has been found to have good intra-rater reliability
[9]. However, few reports are available regarding its inter-
rater reliability. Hundley et al. [19] reported that the Peritron
manometer had high inter-rater reliability, but not all subjects
were evaluated by the same examiners, and the authors stated
that, in the purest sense, an assessment of inter-rater reliability
requires that all subjects be examined by all examiners [19].
Thus, there seems to be a lack of studies truly evaluating the
inter-rater reliability of this device.
If more than one examiner is to assess the participants in
clinical studies, it is essential to assess the inter-rater reliabil-
ity of the measurement method [3]. To date, there seems to be
an immediate need for inter-rater reliability studies of both the
modified Oxford Grading Scale and the Peritron manometer.
In addition, Bo and Finckenhagen [12] questioned the ability
of vaginal palpation to differentiate correctly between differ-
ent degrees of pelvic floor muscle strength, and their results
need further investigation.
The primary aim of this study was to evaluate the inter-
rater reliability of the modified Oxford Grading Scale and the
Peritron manometer. A secondary aim was to compare the
scores obtained with the modified Oxford Grading Scale and
the Peritron manometer for squeeze pressure measurement.
Materials and methods
Study design
This was a test–retest study assessing the inter-rater relia-
bility of the modified Oxford Grading Scale and the Peritron
manometer.
Participants
An initial sample of 20 female university students partici-
pated in the study.All participants signed an informed consent
form, and the study was approved by the institutional research
ethics committee.
Inclusion criteria were: age between 18 and 35 years,
normal body mass index (<25 kg/m2), nulliparous and non-
pregnant, and no gynaecological complaints or disease
verified by at least one medical appointment in the past 12
months. Exclusion criteria were: pelvic organ prolepsis or
reconstructive pelvic surgery, symptoms of vaginal infection,
intolerance to condoms, allergy to the gel used in the proce-
dure, and involvement in pelvic floor muscle training. One
participant reported that she had trained her pelvic floor mus-
cles between the two evaluations, and was excluded from the
study. Thus, the final sample consisted of 19 women.
Fig. 1. Peritron perineometer.
Assessment tools
The modified Oxford Grading Scale [4] quantifies pelvic
floor muscle strength as: 0, no contraction; 1, flicker; 2, weak;
3, moderate; 4, good; and 5, strong.
The Peritron manometer measures vaginal squeeze pres-
sure through a conical sensor covered with a medical silicone
rubber sheath (Fig. 1). The sensor is connected to a hand-
held microprocessor with a latex tube, allowing measurement
of squeeze pressure in centimetres of water (cmH2O). The
occlusive pressure readings from a manometer are a surrogate
measure of strength.
Interventions
An interviewer (PBB) questioned the participants about
their age, weight, height, use of oral contraceptives, level of
physical activity, participation in pelvic floor muscle training,
parity and urinary incontinence.
After verifying that the participants were eligible to take
part in the study, pelvic floor muscle strength was assessed.
Examinations were conducted with the participants in a litho-
tomy position. All women were evaluated twice, first by one
examiner and 30 days later by a second examiner. Both exam-
iners (FDOS and MMF) were trained in this specific protocol
of pelvic floor muscle assessment by a physiotherapist with
11 years of clinical experience and supervision of pelvic floor
physiotherapists. Moreover, both examiners had equivalent
134 C.H.J. Ferreira et al. / Physiotherapy 97 (2011) 132–138
skills in pelvic floor physiotherapy and worked exclusively
in women’s health. Examiner 1 (FDOS) had 4 years of clinical
experience and Examiner 2 (MMF) had 3 years and 6 months
of clinical experience. The interviewer (PBB) remained in the
room to ensure that the same procedures were performed by
the two examiners. The examiners were blinded to the results
obtained by each other.
Vaginal palpation was performed using two fingers. The
ability to contract and relax the pelvic floor muscles was
first evaluated by palpation, asking the subject to pull her
pelvic floor muscles in and up as strongly as possible and
then to relax them completely. When a correct contraction
was verified, the examiner scored it according to the modified
Oxford Grading Scale [7].
After vaginal palpation, the Peritron manometer was
placed with the middle of the probe 3.5 cm inside the vagina
[17]. The device was calibrated to zero before each mea-
surement. The vaginal sensor was not inflated. According to
the manufacturer, inflation is an optional resource that can
reduce the sensitivity of the sensor’s response. The women
were instructed to undertake three maximal pelvic floor mus-
cle contractions sustained for 5 seconds with an interval of
30 seconds, as reported in a previous study [20]. Only con-
tractions with visible inward movement of the perineum were
considered to be valid [21]. Co-contraction of the gluteal and
hip adductor muscles was discouraged, as was the Valsalva
manoeuvre [5,9,22]. At the end of the second evaluation, the
participants were asked if they had done any pelvic floor
muscle training between the two evaluations.
Statistical analysis
Background variables are reported as frequencies and
percentages. The Kappa coefficient was used to assess the
inter-rater reliability of the modified Oxford Grading Scale
[23].
The mean peak value of the three contractions was used
to analyse the inter-rater reliability of the Peritron manome-
ter [20,24]. Bland and Altman limits of agreement [25–29]
were used to compare the measurements obtained by the two
examiners using the Peritron manometer, and the Pearson
correlation test [30] was used to compare the values obtained
with the Peritron manometer and the modified Oxford Grad-
ing Scale.
Results
The mean age of the participants was 24 years (range
21 to 28 years). All the participants were nulliparous White
women who lived in Ribeirão Preto city, Brazil. Mean body
mass index was 21.3 (range 17.1 to 24.7). Seventeen of
the 19 participants (89%) were using an oral contraceptive,
and six (31%) were undertaking regular general physical
exercise. None of the subjects included in the analysis had
done pelvic floor muscle training before participating in the
Table 1
Individual results of two vaginal palpation tests assessed by two physical
therapists. Muscle strength classified by the modified Oxford Grading Scale
(0 to 5), n= 19.
Subject Examiner 1 Examiner 2
12 2
22 3
34 5
43 5
54 4
63 3
72 2
83 3
92 4
10 4 4
11 2 2
12 4 4
13 2 4
14 2 4
15 2 3
16 4 5
17 2 4
18 3 4
19 4 4
κ= 0.33 (95% confidence interval 0.09 to 0.57).
research project or between the two evaluation points. One
woman reported sporadic symptoms of urge urinary incon-
tinence. During palpation, all women included in the study
were able to voluntarily contract and completely relax their
pelvic floor muscles. No women had hypertonic pelvic floor
muscles.
Table 1 shows the pelvic floor muscle strength of each
participant classified by the two examiners using the mod-
ified Oxford Grading Scale. The weighted Kappa was fair
[κ= 0.33, 95% confidence interval (CI) 0.09 to 0.57]. There
was agreement between the examiners for nine of the 19 sub-
jects (47%). No participants were classified as Category 0
or 1 by either examiner. Examiner 2 scored three of the 19
(16%) participants as Category 5; Examiner 1 did not score
any participants as Category 5. In 10/19 (53%) evaluations,
Examiner 2 scored the participant as a higher category than
Examiner 1.
The mean vaginal squeeze pressure of three contractions
for the whole group was 44 cmH2O (95% CI 35.5 to 52.5) in
the first evaluation and 46.7cmH2O (95% CI 37.9 to 55.5) in
the second evaluation. The differencebetween the evaluations
was not statistically significant (P= 0.65, 95% CI −14.46 to
9.13).
Table 2 shows the mean of three maximal contractions for
each participant in the first and second examinations using
the Peritron manometer.
Table 3 shows the mean muscle strength (cmH2O) with
95% CI measured using the Peritron manometer for the six
categories assessed by the modified Oxford Grading Scale for
both examiners. Examiner 1 did not score any participants
as Categories 0, 1 or 5, and Examiner 2 did not score any
participants as Categories 0 or 1.
C.H.J. Ferreira et al. / Physiotherapy 97 (2011) 132–138 135
Table 2
Mean of three maximal pelvic floor muscle contractions (cmH2O) of indi-
vidual participants by two different examiners using the Peritron manometer,
n= 19.
Subject Examiner 1 Examiner 2
1 27.1 30.1
2 33.3 37.3
3 70.4 80.9
4 41.4 40.4
5 36.8 31.9
6 44.3 61.7
7 50.5 26.8
8 50.1 51.5
9 66.8 54.6
10 37.8 56.6
11 42.7 23.7
12 76.4 84.1
13 47.2 44.0
14 20.7 27.9
15 64.0 39.7
16 25.6 64.3
17 16.5 25.8
18 23.9 41.7
19 60.5 63.8
Mean for Examiner 1: 44 cmH2O (95% confidence interval 35.5 to 52.5).
Mean for Examiner 2: 46.7 cmH2O (95% confidence interval 37.9 to 55.5).
Fig. 2 shows the limits of agreement of pelvic floor muscle
squeeze pressure measurements obtained with the Peritron
manometer by the two examiners using the mean of three
maximal readings. In 11 of 19 (58%) cases, the difference
between the examiners was less than 10 cmH2O.In7of19
(37%) cases, the difference was more than 15 cmH2O. It is
estimated that in 95% of each test, the examiners will not
exceed the limits of agreement, showed in the Fig. 2.
Fig. 3 shows a scatter plot with the values scored by the
two examiners for the six categories of the modified Oxford
Grading Scale, and correlation with the values for pelvic floor
muscle squeeze pressure measurements obtained with the
Peritron manometer. The results of Pearson’s correlation test
Table 3
Mean muscle strength (cmH2O) with 95% confidence intervals (CI), mea-
sured with the Peritron manometer, in the six categories assessed by the
modified Oxford Grading Scale by the two examiners.
nMean 95% CI
Examiner 1
No contraction 0 – –
Flicker 0 – –
Weak 9 41.0 27.1 to 54.8
Moderate 4 39.9 22.0 to 57.8
Good 6 51.2 29.6 to 72.9
Strong 0 – –
Examiner 2
No contraction 0 – –
Flicker 0 – –
Weak 3 26.9 18.9 to 34.8
Moderate 4 47.5 29.5 to 65.5
Good 9 47.8 33.2 to 62.4
Strong 3 52.1 11.2 to 92.8
Fig. 2. Bland–Altman limits of agreement comparing the mean of three
measures obtained using the Peritron manometer by the two examiners.
were r= 0.25 (95% CI −0.23 to 0.63) for Examiner 1 and
r= 0.51 (95% CI 0.08 to 0.78) for Examiner 2.
Discussion
This study found fair inter-rater reliability for the modified
Oxford Grading Scale, and moderate inter-rater reliability for
the Peritron manometer. There was agreement between the
examiners for nine of 19 subjects (47%) using the modified
Oxford Grading Scale. Using the Peritron manometer, the
difference between the examiners was less than 10 cmH2Oin
11 of 19 (58%) cases. There were no differences between the
Oxford Grading Scale categories compared with the results
obtained with the Peritron manometer.
The results of studies evaluating inter-rater reliability of
other palpation scoring systems and squeeze pressure using
Spearman’s correlation rho range from r= 0.60 to r= 0.90
[13,19,31–34]. The findings of Bo and Finckenhagen [12]
showed only acceptable (fair) inter-rater reliability for the
modified Oxford Grading Scale using Cohen’s Kappa (0.37),
despite a higher Spearman’s rho value (0.70). The present
findings were similar using Cohen’s Kappa (0.33). Spear-
man’s rho was not used in the present study as it is not able to
reveal systematic variations between two examiners, and may
overestimate reliability, as shown by Bo and Finckenhagen
[12].
The modified Oxford Grading Scale was used in this study
because it is commonly used in clinical physical therapy.
After this study was concluded, Slieker-ten Hove et al. [13]
published a face validity and reliability study of the first dig-
ital assessment scheme of pelvic floor muscle function to
conform with the standardised terminology of the Interna-
tional Continence Society. To evaluate voluntary pelvic floor
muscle contraction and estimate strength, this scale used the
136 C.H.J. Ferreira et al. / Physiotherapy 97 (2011) 132–138
Fig. 3. Values estimated by the two examiners for the six categories of the modified Oxford Grading Scale, and correlation with the values obtained for pelvic
floor muscle strength with the Peritron manometer (cmH2O).
Brink score [32]. The authors stated that inter-rater reliability
of this new scale was generally disappointing, but some items
were good including the evaluation of voluntary contraction
with the Brink score (κ= 0.64).
Although the modified Oxford Grading Scale allows the
assessment of other aspects of pelvic floor muscle function,
the only function that could be compared in this study was
the strength (squeeze), since a perineometer was used to test
the criterion validity of this scale [12]. The modified Oxford
Grading Scale and manometry do not measure exactly the
same aspects. According to Bo et al. [6], one of the difficul-
ties of measurement using the modified Oxford Grading Scale
is that it produces one value for occlusion and lift in one scale.
The last three categories of the scale require the examiner’s
palpating fingers to be sufficiently sensitive to notice not only
occlusion but also the lift component. The lack of complete
equivalence of these two parameters (squeeze and lift) mea-
sured by the two assessment tools may explain the lack of
linearity between them and the low agreement obtained by
the two examiners, especially for the last two categories of
the modified Oxford Grading Scale, in the present study.
The results of muscle evaluation depend on the experi-
ence of the testers and the position of the subject being tested
[12]. The authors controlled these factors as much as possi-
ble, and the two examiners were skilled physical therapists
with similar experience in conducting this type of examina-
tion. In addition, they were blinded to each other’s results.
All the participants were instructed in pelvic floor muscle
contraction, and only correct contractions with perineal ele-
vation were accepted [16,21]. Some studies have used the
highest of three measurements for vaginal squeeze pressure to
determine intra- or inter-rater reliability [2,9,12], while oth-
ers, including the present study, have used the mean of three
measurements due to possible variations related to learning
and fatigue [20,24].
For inter-rater reliability of the Peritron manometer, this
study found that the differences between examiners were less
than 10 cmH2O in 11 of 19 (58%) cases, indicating accept-
able agreement. However, in seven of 19 (37%) cases, the
differences were more than 15 cmH2O. The only other study
identified that assessed the inter-rater reliability of the Per-
itron manometer found high correlation between the results
of the two examiners [19]. The study included 100 women
(18 nulliparous and 82 parous). However, a subgroup analysis
showed that correlation between examiners was unaffected
by parity [19]. The authors explained issues that may have
influenced their results, including the short interval between
the two examinations and the fact that the examinations
were performed by multiple examiners. Furthermore, not all
subjects were evaluated by the same examiners [19]. The
statistical methods used in the present study were different
from the study mentioned above, making comparison diffi-
cult. Bland and Altman’s limits of agreement were used in
the present study as it has been demonstrated that the use
of correlation tests is inappropriate for the determination of
reliability and may overestimate the results [25–27].
In the present study, all subjects were examined by the
same two examiners, with an interval of 30 days between
the two evaluations. This was done to prevent fatigue from
influencing the measurements [9], but mostly for practical
reasons. A shorter interval between the two examinations
would be better, but it was impracticable for the participants
to return to the place where examinations were performed
before 30 days. This long interval may have given them time
to train their pelvic floor muscles, although they were told
not to do so between the two evaluations. Exercise between
the two tests was an exclusion criterion, and one woman was
excluded because she reported that she had trained. For the
whole group, the mean values of vaginal squeeze pressure
assessed by the two examiners did not differ, but Examiner 2
always scored the participants with higher categories on the
modified Oxford Grading Scale than Examiner 1. Given this,
it is not possible to guarantee that no learning effect occurred,
although an increase in muscle strength is only expected after
5 months of intensive pelvic floor muscle training [35]. Since
the results can be time- and rater-dependent, and given that
C.H.J. Ferreira et al. / Physiotherapy 97 (2011) 132–138 137
the time effect cannot be separated from the inter-rater effect,
this long interval represents a limitation of the study.
The results of this study agree with the findings of Bo and
Finckenhagen [12] showing that palpation scores using the
modified Oxford Grading Scale did not differentiate pelvic
floor muscle strength. The same methodology was used
although the vaginal pressure manometers were different.
The use of different types of perineometer generates differ-
ent results that should not be compared [20,36]. In contrast,
Isherwood and Rane [10] found good agreement between
the modified Oxford Grading Scale and the PFX9100C
perineometer (Cardio-Design, Victoria). However, the per-
ineometer they used reported squeeze pressures ona0to
12 point scale, and in contrast with the present study, one
examiner only used the modified Oxford Grading Scale and
the other performed the evaluations with the perineometer.
Other authors have found good correlation between differ-
ent vaginal palpation scales and vaginal squeeze pressure
[8,19,36,37]. A possible explanation of why the present study
did not find any difference between the scores for vaginal pal-
pation and vaginal squeeze pressure could be due to the small
sample size and to the fact that some categories of the modi-
fied Oxford Grading Scale were not scored by the examiners.
Another limitation of the present study is that the findings
may only be valid for nulliparous women at a very young
age, and the results may differ in older women with pelvic
floor disorders.
Although the data analysis did not indicate that the group
of women evaluated had generally weak pelvic floor mus-
cles, more than 35% had their pelvic floor muscle contraction
scored as weak or moderate by the two examiners. Dietz et al.
[38] found that almost half of young and nulliparous women
contracted their pelvic floor muscles unsatisfactorily or not at
all unless they received instructions [38]. This indicates that
the evaluation of pelvic floor muscles in young nulliparous
women is essential, not only in research aiming to determine
normal values of pelvic floor muscle strength, but also to
evaluate preventive guidelines related to improvement of the
ability to contract the pelvic floor muscles and to pelvic floor
muscle training programmes in this population.
Despite the small sample size, the excessive homogene-
ity of the sample and the long interval between evaluations,
the present results indicate that the inter-rater reliability of
the Peritron manometer is acceptable and it can be used in
re-evaluations performed by different examiners in clinical
practice. However, for research purposes, the ideal situation
is for the same examiner to assess and re-assess subjects. The
modified Oxford Grading Scale should not be used by differ-
ent examiners and does not adequately correlate with vaginal
squeeze pressure measurements in nulliparous women.
Conclusion
This study found fair inter-rater reliability for the modified
Oxford Grading Scale and moderate inter-rater reliability for
the Peritron manometer. For both assessment tools, the ideal
situation is for the same examiner to assess and re-assess sub-
jects. Despite the fact that the modified Oxford Grading Scale
and the Peritron manometer do not evaluate exactly the same
aspects of pelvic floor muscle function, the Oxford Grad-
ing Scale was not able to classify the degree of contraction
correctly when compared with manometer readings. Vaginal
palpation is important in assessing the correctness of a pelvic
floor muscle contraction, but this study does not support the
use of the modified Oxford Grading Scale as a reliable and
valid method to measure pelvic floor muscle strength. Further
test–retest studies in larger and more heterogeneous samples
are warranted to substantiate these findings. The develop-
ment of new pelvic floor muscle strength assessment tools
and refinement of the existing tools is essential for reliable
evaluations performed by more than one examiner.
Acknowledgements
The authors gratefully acknowledge the Foundation for
the Support of Research of São Paulo State and Professor
Edson Zangiacomi Martinez from the Center for Quantitative
Methods for valuable advice with the statistical analysis.
Ethical approval: Institutional Research Ethics Committee of
the University Hospital of Faculty of Medicine of Ribeirão
Preto- University of São Paulo (FMRP-USP) (Protocol No.
12188/2007).
Conflict of interest: None declared.
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