Research RepoH
The Gross Motor Performance Measure: Validity and
Responsiveness of a Measure of Quality of Movement
Background and Purpose. Zbis article presents the results of a study to validate a measure of gross motorperformance for its capacity to detect changes in
the quality of movement in children with cerebral palsy aged 0 to 12 years.
Subjects and Methods. On two occasions, 4 to 6 months apart, physical therapistsfrom three children's treatment centers assessed 106 children with cerebralpalsy, 18 children who had sustained a n acute head injury, and 29 nondisabled children. Validity was demonstrated by comparing changes on the
measure across diagnoses, severity, and age groups. Results. Several a priori
hypotheses were supported; however, relationships with parent and therapist
ratings were not clearly demonstrated. Conclusion and Discussioa Zbe measure was found to be differentially responsive to changes in '%tablenand "responsiue"groups. (Boyce WF, Gowland C,Rosenbaum PL, et al. Zbe Gross Motor
Performance Measure: validity and responsiveness of a measure of quality of
movement. Phys Zber. 1995; 75.603- 613.1
William F Boyce
Carolyn Gowland
Peter L Rosenbaum
M a y Lane
Nancy Plews
Charles H Goldsmith
Dianne J Russell
Virginia Wrlght
Shelley Potter
Deborah Harding
Key Words: Cerebral palsy, G m motor behavior, Measurement, Movement,
Validity.
Research in the field of cerebral palsy
(CP) has been hampered by a lack of
reliable, valid, and responsive measures of physical function. In particular, before studies of treatment efficacy
or effectiveness can be implemented,
there is a need for good measures of
gross motor behavior.'
Gross motor behavior in children with
CP has been conceptualized as having
two main features: function and performan~e.~
We use the term "gross
motor function" to describe the accomplishment of motor activities, or
how much the child does, for example, standing independently for 10
seconds. In this context, "function"
does not necessarily refer to activities
that are purposeful to the child or
performed in everyday settings. Instead, functional activities are defined
as traditbnal gross motor milestone
behaviors that can be tested in a standardized manner.
ments to measure change in motor
function and performance over time.'
The term "gross motor performance"
describes the quality of motor activities, or how well the chdd does the
activity, for example, the degree of
stability when standing. The importance of motor performance to overall
motor behavior in children is reflected
in the work of Bobath,3 Rood,4and
Bly.5 Numerous authors 6-8 have described the need to develop instruments to measure this feature.
The Gross Motor Function Measure
(GMFM) has demonstrated high levels
of validity, reliability, and responsiveness in the assessment of motor function in children with CP.1° The GMFM
consists of 88 items organized into five
dimensions: lying and rolling; sitting;
crawling and kneeling; standing; and
walking, running, and jumping. Although these items do not assess children within different environmental
contexts, nor do they represent activities chosen by children themselves,
they were chosen by therapists as
important for developmental progress
and amenable to change.10~"During a
previous study, we determined that an
additional instrument was required to
measure performance, or the qualitative aspects of motor behavior that are
characteristic of children with CP but
Since 1984, researchers at McMaster
University, Queen's University, and the
Hugh MacMillan Rehabilitation Centre
in Ontario, Canada, have conducted a
series of studies to develop gross
motor measures for use with children
with CP. The purpose of these studies
has been to design and validate instru-
Physical Therapy /Volume 75, Number 7 /July 1995
603 / 27
that are not measured adequately by
other motor measures.12
Initially, we developed the Gross
Motor Performance Measure (GMPM)
after reviewing the literature relative to
attributes of gross motor performance.
Definitions were written for 33 attribute~.~'
Through nominal group
process meetings, 30 developmental
therapists from five children's treatment centres in southern Ontario
helped to reduce the number of attributes to 5 and to develop attribute
scales.l3 An international panel of
experts working in academic and
clinical settings provided judgments on
content validity of the GMPM using a
Delph consensus method. Results
indicated that the GMPM had satisfactory completeness, clarity, and potential for evaluating changes in motor
performance.l4
The GMPM is a criterion-referenced
observational instrument that can be
administered with a minimum of
equipment in less than 1 hour, depending on assessor skill, developmental stage, and cooperation of the
child. The measure consists of 20
items derived from the GMFM, each of
which is matched with three designated attributes of performance. Possible attributes to be assessed include
alignment, stability, coordination,
weight shift, and dissociation. Children
are assessed only on items in which
they can achieve at least a partial
GMFM score, meaning that they can
initiate an activity, thereby allowing an
assessment of motor quality. Thus,
some children have motor performance assessed on all 20 items,
whereas others are assessed on as few
as 2 or 3 items. Attributes are scored
on individualized five-point scales
varying from 1 ("severely abnormal")
to 5 (''consistently normal"). (See Appendixes 1 and 2 for attribute d e h tions, sample GMPM item, and scale.)
Raw scores are summarized into a
WF Boyce, MSc, PT, is Assistant Professor, School of Rehabilitation Therapy and the Departments
of Paediatrics and Community Health and Epidemiology, Queen's University, Kingston, Ontario,
Canada K7L 3N6 (boycew@post.queensu.ca).Address all correspondence to Mr Boyce.
C Gowland, MHSc, PT, is Associate Professor, School of Occupational Therapy and Physiotherapy,
Faculty of Health Sciences, McMaster University, Hamilton, Ontario, Canada L8N 325.
P Rosenbaum, MD, is Professor of Paediatrics, Faculty of Health Sciences, McMaster University,
and Director of Paediatrics, Chedoke Child and Family Centre, Chedoke-McMaster Hospitals,
Hamilton, Ontario, Canada.
M Lane, PT, is Physiotherapist, Halton Parent-Infant Program, Oakville, and Clinical Consultant,
Neurodevelopmental Clinical Research Unit, McMaster University.
N Plews, PT, is Research Physiotherapist, Chedoke-McMaster Hospitals.
CH Goldsmith, PhD, was Professor, Department of Clinical Epidemiology and Biostatistics, Faculty
of Health Sciences, McMaster University, when this study was completed. Dr Goldsmith is currently with St Joseph's Hospital/McMaster University, Center for Evaluation of MedicinesBiostatistics, Martha Wing, 50 Charlton Ave E, Hamilton, Ontario, Canada L8N 4A6.
DJ Russell, MSc, is Research Coordinator (Neurodevelopmental Clinical Research Unit), Department of Clinical Epidemiology and Biostatistics, Faculty of Health Sciences, McMaster University.
V Wright, MSc, PT, is Research Physiotherapist, Hugh MacMillan Rehabilitation Centre, Toronto,
Ontario, Canada M4G 1R8.
S Potter, BSc, PT, is Senior Therapist, Niagara Peninsula Children's Centre, St Catharines, Ontario,
Canada L2R 7A7.
D Harding, BSc, PT, is Physiotherapist, Metropolitan Toronto School Board, Toronto, Ontario,
Canada M2P 1B6.
This study was approved by ethics review boards of Queens University, McMaster University, and
the Hugh MacMillan Rehabilitation Centre.
This study was supported by funding from the National Health Research and Development Proesam (Grant No. 6606-3740)
.
. of Health and Welfare Canada. The studv was coordinated at the
Child ~ e v e l o ~ m e Centre,
nt
Hotel Dieu Hospital, Department of ~ a e i a t r i c s Queen's
,
University,
Kingston, Ontario, Canada.
total score and subscale attribute
scores. These scores are expressed as
percentages of the maximum possible
score relative to the number of items
performed.
Validation Hypotheses
Because there is not an accepted criterion evaluative measure of overall
motor performance for children with
CP,12direct tests of criterion validity
could not be conducted. Hypotheses
were dficult to develop because there
is minimal motor control theory applicable to this heterogeneous population.l5 In addition, there are no longitudinal studies of the natural history of
motor performance in children with
CP. Thus, we developed hypotheses
from the knowledge base of investigators and therapists experienced in
working with this population. In addition, experience with the GMFM development gave us information and
ideas we could use to formulate hypotheses about potential change in
motor performance.
We believe that construct validity of
the GMPM could be tested by formulating a series a priori
about how change scores on the
GMPM would be associated with
different study groups and with
changes in function. We expected that
diferences in performance of motor
activities in different groups of children
could be assessed by comparing
scores among groups of children with
CP, children with other neurological
problems, and children without neurological problems. We expected that
the GMPM change scores would be
greatest in a group of children with
acute neurological injuries, such as
head injury, as these children often
recover rapidly from their injuries and
frequently have marked improvements
in performance attributes such as
coordination and stability.
-
-
Change
in children
disabilities were expected to be minima1 because these children should
already have normal quality of movement, although there may be slight
changes in performance as children
This article was submitted December 3, 1993, and was accepted February 24, 1995.
28 / 604
Physical Therapy / Volume 75, Number 7 /July 1995
learn new motor behaviors such as
walking.
Developmental changes in motor skills
and performance generally slow as
children mature; therefore, younger
children with CP were expected to
show more change in GMPM scores
than older children. Change scores in
children with CP were expected to be
greater in those with d d e r impairments or disabilities and less in those
with more severe problems. Classification of impairment severity into mild,
moderate, and severe categories is a
common, yet relatively untested, clinical and research practice. Recent evidence from plots of GMFM scores
against clinician's assessments of "severity" in children with CP, however,
shows distinct patterns of motor function in these dfierent groups (Rosenbaum PL, Russell DJ; unpublished
research). Although reliability data are
not available, the face validity of this
categorization of severity for motor
function may extend to the assessment
of gross motor performance, which is
also a strong characteristic of movement of children with CP.
We anticipated that changes in the
GMPM were likely to be positively
correlated with changes in function as
measured by the GMFM because improvement in a child's quality of
movement, or performance, could
contribute to change in the child's
gross motor skills. We also recognized
that the relationship between change
in motor function and change in performance would not necessarily be
strong.
Concurrent validity of the GMPM was
tested through comparison with independent parent and therapist ratings of
motor performance. In a previous
study,1° measures of parent and therapist ratings of children's motor function were demonstrated to be reliable
in this population. We expected therapist ratings to correlate more highly
with the GMPM than parent ratings
because therapists were familiar with
the concepts of performance used in
the GMIJM,whereas parents were not.
Parents' judgments of changes were
expected to be based on their evaluaPhysical Therapy / Volume 75, Numbe
tion of what the child does in daily life
and thus more focused on function
than performance.
Five hypotheses were formulated to
test the validity of the GMPM:
1. Hypothesis l-Children with head
injuries will have greater changes in
GMPM scores over time than children in other groups. Nondisabled
children will show smaller changes
than children in other groups.
2. Hypothesis 2-Children with CP
classified by therapists as "mild or
"moderate" will have greater
changes in GMPM scores over time
than those with CP classified as
"severe."
3. Hypothesis %Infants with CP will
show more changes in GMPM
scores over time than toddlers and
older children.
4. Hypothesis 4-GMPM change scores
will have a low to moderate correlation ( r r 30) with GMFM change
scores.
5. Hypothesis 5-Correlations between
change scores on the GMPM instrument and therapist ratings of
change will be moderate ( r r .55).
Correlations of GMPM change
scores with parent ratings of
change will be slightly lower ( r r
.45).
Responsiveness
An evaluative instrument is responsive
if there is a high likelihood of detect-
ing a treatment effect even if that effect
is small.16A responsive measure will
allow one to be confident of detecting
a change, through inspection af the
change score, should a change actually occur. An appropriate measure of
responsiveness can be obtained by
relating the variability in test scores of
stable individuals to the dfierence in
scores of individuals who are
changing.16
The objective of this validation study
was to examine the measurement
properties of the GMPM. Validity (con-
struct, concurrent), reliability (interrater, intrarater, test-retest), and responsiveness of the instrument were
investigated with the assumption that
the primary use of the GMPM would
be to evaluate change in the performance of common gross motor activities over time. This assumption has
implications for the criteria used to
judge the measure.17 The purpose of
this article is to report the validity and
responsiveness findings of that study.
Results from reliability analyses are
reported elsewhere (see article by
Gowland and colleagues in this issue
of Physical nerapy)).
Method
On the basis of available ~nformation
regarding variability in motor performance scores and possible effect sizes,
we estimated that we would need a
sample size of 180 children to appropriately examine our hypotheses. We
initially planned to recruit 120 children
with CP, 30 chddren who had sustained an acute head injury (HI), and
30 children without neurological problems from three children's treatment
centers. The latter two groups were
included to provide comparative samples in which changes in gross motor
performance were likely to be either
dramatic (HI) or minimal (no disability). We considered the sample size
adequate for analysis because onetailed 95% confidence intervals would
vary from .74 to .84 if validation correlations of r > .80 were obtained for an
overall effect. We contend that this
correlation level is acceptable when
using intraclass correlation coefficients
(ICCs) and is based on our experience
in previous validation studies of the
GMFM.7
The final enrollment was 106 in the
group of children with CP, 18 in the
group of children with HI, and 29 in
the group of children without neurological problems, for a total of 153
children. This final sample size was
limited by the willingness of children
and their families to participate in a
lengthy study requiring multiple assessments. The children with CP and
HI were receiving various forms and
intensities of therapy. Because we
I
Table I. Validation Study Sample
Severity of Impairment
Diagnostic
Group
Age
(Y)
Cerebral palsy
0 -2
8
3- 4
10
15
5- 6
2
13
7-1 2
5
11
Mild
Moderate
Severe
Total
15
Total
25
54
Head injury
0-19
6
7
Nondisabled
0-2
3- 6
Total
wanted to study the ability of a measure to detect changes in motor performance, and not to attribute any
changes in performance to therapeutic
efficacy, we did not consider it important to classlfy children according to
treatment status.
Children with CP were selected to
provide a range of age and severity of
neurological involvement. Children
with either CP or HI were categorized
into mild, moderate, and severe
groups by the referring therapist. This
categorization was based on criteria
for severity that were in common use
at the participating study centers. Children in the HI group were all in the
early (<3 months postinjury) stages of
recovery (Tab. 1).
Physical therapists who worked regularly with children with neurological
impairments participated in the study.
Proficiency in administration of the
GMFM was a requirement for participation because the GMPM and the
GMFM are linked. Thirty therapists
were initially trained in administration
and scoring of the GMPM and GMFM
in 2-day training sessions. Training
was facilitated by using a series of
videotapes of children with CP, including various ages, types, and levels of
function, as well as nondisabled children. Therapists were trained by the
investigators in the use of the measures to a criterion Kappa agreement
level of at least ~ = 0 . 6indicating
,
mod-
erate agreement with the investigators'
consensus-based ratings of the videotapes,18 before commencing to enroll
children in the study. This training
methodology was described in an
earlier report. l R Therapists also practiced administering the measure on
non-study children to improve their
familiarity with the instrument.
After receiving signed consent from
parents or guardians, the children
were assessed at the same time with
the GMPM and GMFM on two occasions 4 to 6 months apart. The tests
were administered on both occasions
according to the protocols outlined in
the GMFM and GMPM administration
guidelines. Standardized parent rating
scales and therapist rating scales were
independently completed prior to
each assessment to give separate parent and therapist judgments of each
child's gross motor performance. For
these measures, a Likert scale is used
to judge the child's current motor
performance and change in motor
performance over time for the concurrent validity analysis. A similar set of
questionnaires was used in the GMFM
validation study and were shown to
reliably assess change in gross motor
function by parents (n=23, ICC=.92)
and by therapists (n= 23, ICC= .96).11
To assess responsiveness, parents and
therapists were asked to rate the
child's overall change in motor performance before the second administra-
tion of the test. A separate 15-point
scale was used to rate the child's motor performance, from -7 (large negative change), through 0 (no change),
to +7 (large positive change). We
classdied children as belonging to a
"responsive" group if they were
judged by either therapists or parents
as having improved in performance
(ie, a score between + 2 and +7). A
"stable" group was considered to be
those children who were identified by
either the parents or therapists as "not
having changed" or as "changing only
a very small amount" (ie, - 1, 0, + 1).
A responsive measure should show
little variability due to time in a "stable" group and greater variability due
to time in a "responsive" group. Further details of the study design, including reliability assessment methods, are
reported elsewhere.'9
Data Analysis
Summary scores were calculated to
create a GMPM total score and five
individual attribute scores. A high
score indicates a comparatively normal
motor performance. To calculate an
alignment score, for example, raw
scores for the alignment attribute are
summarized across all motor items in
which alignment appears. This score is
expressed as a percentage of the maximum possible score relative to the
number of times the child was assessed on alignment. This method
ensures that the level of motor function, or ability to do motor activities,
does not affect the scoring of the performance of those activities. Thus,
young children without disabilities
may score low on function but high
on performance. Older children with
severe disabilities may score low on
function and performance. Only total
score data will be reported here.
Because 3 children were lost to
follow-up and 7 children's data were
incomplete, the data from 143 children
were available. This sample comprised
9 children with CP, 17 children with
HI, and 27 children with no disabilities. Data transformation was not required, and no adjustment was made
for multiple testing.
Physical The]:spy / Volume 75, Number 7 /July 1995
Table 2.
Cross Motor Pe$onnance Measure Mean Total Scores for All Subjects
Categorized by Diagnosis
Diagnostic Group
--
Head Injury
Cerebral
Palsy
Nondisabled
Time 1
62.1
20.2
52.2
15.1
Time 2
69.4
17.7
54.5
16.2
7.3
9.4
2.3
6.1
Change
t(16)=3.22
t(98)=3.79
P, = ,0053"
P, = .0003'
Two-tailed probability, P25.O5.
Hypotheses 1 (diagnostic differences),
2 (severity differences) and 3 (age
differences) were examined using
t tests and analyses of variance
(ANOVAs) to detect differential
changes in GMPM scores over time.
Hypotheses 4 (GMPM-GMFM correlations) anti 5 (therapist/parent-GMPM
correlations) were examined using a
correlation analysis. In the responsiveness analysis, a repeated-measures
ANOVA on time 1 and time 2 scores
for both the "stable" group and the
"responsive" group was done. The F
statistics from these two ANOVAs
were used to calculate an ICC for each
group.18A Fisher Z transformation was
used to compare the two correlation
coefficients to determine whether they
were ditferent. The level of statistical
significance was set at P21.05 (twotailed probability) for t-test and
ANOVA analyses and at P,S.05 (onetailed probability) for correlation analyses.
Results
Failure to enroll the full planned sample size had some effecton the statistical power available for certain subgroup analyses. Power, however, is
also affected by the size of the effect
and by acceptable levels of type I and
I1 errors. Small effect sizes, such as
those that may occur in motor performance, are more difficult to detect
than larger ddferences. Similarly, in a
heterogeneous population such as the
children with CP in this study, the
likelihood of detecting differences is
decreased. On the basis of available
information, we were able to estimate
an appropriate sample size at the
outset of the study. It was not possible, however, to predict the variability
and relatively small effect sizes of
motor performance in the children
with CP. For this reason, and because
we examined fewer children than we
had planned, the power to detect
Merences in some analyses was less
than expected. This methodological
problem is common in preliminary
studies of phenomena. Thus, we are
cautious in the interpretation of these
data and focus on trends that may
direct future research.
Hypothesis 1
This hypothesis was strongly supported. Analysis of variance indicated
that total scores for each diagnostic
group differed from each other at time
1 and time 2 (Tab. 2). High scores for
the nondisabled children reflected
their normal movement quality. Lower
scores for the children with HI reflected impairment of many attributes.
Children with CP had the lowest
scores, with impairment of movement
quality in all attributes.
Changes in GMPM total scores (time
2-time 1) supported the hypothesis
that the HI group would show more
change than the CP group and that
Physical Therapy / Volume 75, Number 7 /July 1995
the nondisabled group would show
less change. Paired t tests revealed that
all groups changed between assessments, although the greater change in
the HI group (7.3 units) reflects the
rapid change in movement quality that
may be seen in children recovering
from head trauma. The CP group also
showed change (2.3 units) but of
smaller magnitude. This small degree
of change illustrates the expected
development in motor performance
over a short period of time in a
chronic condition such as CP. The
nondisabled group was not expected
to change dramatically in their motor
performance (0.7 units), although their
motor function was expected to
increase.
Hypothesis 2
This hypothesis was supported by
results that revealed that in the CP
group total scores differed depending
on the severity of condition (Tab. 3).
Time 1 and time 2 scores were highest
for the mild impairment group and
lowest for the severe impairment
group. This finding indicates that the
classfication of CP by severity may be
based at least partly on movement
quality. Analysis of variance indicated
that change in total scores was not
found to be dependent on severity
(F=1.41; df =2,98; P2=.2491). We
interpret this finding with caution
because of the low statistical power
(0.24) available to detect differences.
Change in scores for both mild impairment (2.8 units) and moderate impairment (2.9 units) groups was small but
statistically sigdcant. The group with
severe impairment showed no change
(0.5 units) between assessments.
Hypothesis 3
The initial hypothesis, that changes in
GMPM scores would be greatest for
infants and less for older children with
CP, was not supported by the data,
yet this interpretation must be tempered by a general lack of power in
the analyses. Analysis of variance
indicated that total scores did not differ
across age groups at either the first or
second assessment (Tab. 4). Similarly,
the change in total scores did not
-
3 to 4 years and greater than 7 years.
Table 3. Gross Motor Performance Measure Mean Total Scores for Children With
Cerebral Palsy Categorized by Severity of Impainent
Severity of Impairment
Mild
Moderate
Severe
(n=23)
(n=53)
(n=23)
x
X
SD
SD
X
SD
F
df
67.8
11.2
53.1
9.6
34.7
9.9
62.8
2,96
.OOOle
Time2
70.6
11.9
56.0
9.6
35.2
11.7
64.2
2,96
.OOOle
Change
2.8
6.1
2.9
6.0
0.5
6.2
2,98
.2491
t(22)=2.21
t(52)=3.55
t(22)=0.35
P2=.037Ea
P2= .00oaa
P2= ,7297'
Two-tailed probability, P,S.05.
differ across age groups (F=0.23;
df =3,98; P2=,8753). Paired t tests
within each age group, however,
revealed that scores for children older
than 7 years did change (t[21]=3.09,
P2=,0055). Power in these analyses
varied from 0.07 to 0.21.
This initial finding was contrary to our
expectation that the greatest improvement in motor performance would
occur in younger children with CP. An
ANOVA was conducted to determine
whether there was an interaction of
age and severity of impairment. Mean
change scores were calculated for
each age severity subgroup (Tab. 5).
Within severity groups there was no
difference in mean change scores for
the various age groups. This finding is
-
consistent with the previous results.
Within age groups, however, the 3- to
4year-old children showed differences
between the mild, moderate, and
severe impairment groups (F=4.47;
df =2,32; P2=.0194). The positive
change in the 3- to 4-year-old moderate impairment group (4.2 units)
(t[14]=3.1, P2=,0085) was apparently
balanced out in the earlier age analysis
by the negative change (-2.5 units) in
the 3- to 4-year-old severe impairment
group. Similarly, the positive change
in the >7-yearald moderate impairment group (4.1 units) (t[10]=2.9,
P,= .0167) was sufficient to influence
the results of the entire group of older
children. Thus, the greatest change in
motor performance occurred in children with moderate CP at the ages of
Table 4.
Gross Motor Perfonance Measure Mean Total Scores for Children With
Cerebral Palsy Categorizrd by Age
Time1
53.1
13.6
52.1
17.5
53.0
14.7 50.8
14.0
0.11
3,95
Time2
55.3
14.2
54.0
18.7
55.1
15.6 54.1
15.6
0.04
3,95
,9893
2.2
6.2
1.9
6.0
2.1
4.9
0.23
3,98
,8753
Change
7.6
3.3
t(25)=1.78
t(32)=1.83
t(l7)=1.19
t(21)=3.09
P2=.0872
P2=.0766
P2=.2504
P2=.0055'
Two-tailed probability. Pzs.05
32 / 608
6-year-old mild impairment group
(4.2 units) did not reach statistical
significance. The small number of
children (n=2) in this group likely
affected the power (0.20) of the analysis to detect change.
p2
Time1
.41
A comparatively large change in the 5-
,9541
The two-way ANOVA of age X severity
indicated that the amount of change in
each age group did not depend on
the severity of CP (F=0.86; df=5,98;
P2=.5109).These preceding analyses,
however, may be questioned because
of the small sample size in the subgroups and the &all effect sizes,
which resulted in a lack of statistical
power (0.07-0.20).
Hypothesis 4
The hypothesis that change scores
between the GMFM and GMPM would
be moderately correlated was partially
supported (Tab. 6). At the first assessment, GMFM total scores correlated
with GMPM total scores for the HI
group at .18, the CP group at .72, and
the nondisabled group at .64. The low
correlation for the HI group was due
to consistently high GMFM scores and
variable GMPM scores. Ddferent severity groups of the CP sample yielded
low, but usually significant, correlations from .25 to .45. Different age
groups also yielded significant correlations from .56 to .89.
At the second assessment, similar
correlation patterns were observed,
with higher-correlations in the nondisabled group (r=.81) and the CP
group ( r = .go). The GMPM change
scores, however, were not highly
correlated with GMFM change scores
and ranged from .17 to .23. Differential
rates of change in function and performance could account for these low
correlations. The low correlations may
also be consistent with problems of
low reliability of change scores, which
compound any measurement errors at
both assessment points.21
These data generally support our
contention that motor performance is
related to, yet distinct from, motor
function. It appears that the GMFM
Physical Therapy / Volume 75, Number 7 /July 1995
Table 5.
Gross Motor Perjormance Measure Mean Change Total Scores for Children With Cerebral Palsy Categorized by Age and Severity of Impairment
Severity of
Impairment
0-2
x
SO
>7
5-6
3-4
x
SO
X
SO
X
SD
F
df
Table 7.
Correlations Between
Change on Gross Motor Performance
Measure (GMPM) and Gross Motor Function Measures (GMFM) and Change in
Quality Judged by Parents and
Therapists
P,
Parent
(n=el)
Mild
2.6
Therapist
(n=81)
8.2
(n=7)
Moderate
1.6
Hypothesis
6.3
GMPM change
(n=14)
Severe
3.1
GMFM change
8.2
(n=5)
.45
-.06
.44'
.55
.22
.40
"One-tailed probability, P,5.05.
F=0.12
df =2,25
P2= ,8874
'Two-tailed probability, P2s.05
and GMPM are measuring dfierent
constructs of motor behavior.
Hypothesis 5
The hypothesis that the correlations
between the GMPM change scores
and the therapist ratings of change
would be moderate is not supported
by the data (Tab. 7). Correlations
between GMPM change scores and
judgments of parents ( r = -.06) and
therapists ( r = .22) were low. To determine whether judgments were being
Table 6.
Correlations Between Gross Motor Function Measure and Gross Motor
Performance Measure Total Scores for Various Study Groupsa
n
Time 1
Group
Nondisabled
Head injury
Cerebral palsy
Severity of impairment
Mild
Moderate
Severe
Age (Y)
0 -2
Time 2
Change
made on the basis of changes in gross
motor function as we have defined it
rather than performance, correlations
were also calculated for GMFM
change scores. These correlations
were moderate and significant for
parent ratings ( r = .44) but not for
therapist ratings (r=.40). These results
indicate that structured assessments of
gross motor performance as measured
by the GMPM were not strongly
l~nkedwith clinicians' perceptions of
changes in quality of movement.
Responsiveness
Through analysis of the therapists'
responsiveness subscales, we identified subgroups of 36 "stable" and 60
"responsive" children with CP (Tab. 8).
The "stable" group showed no difference between first and second assessments in total GMPM scores (F= 2.13;
df=1,35; P2=.1533).This finding
indicates that the "stable" group had
little variability in GMPM scores over
time and were not changing in motor
performance. The "responsive" group,
however, showed change in GMPM
scores between the first and second
assessments (F= 12.30; df = 1,59;
P2=.0009). Thus, changes in GMPM
total scores accurately reflected therapist judgments of overall change in
performance in children with CP.
3- 4
5- 6
>7
"Hypothesis r 2 . 3 0 .
b~ne-tailedprobability, P , s . 0 5
Physical Therapy / Volume 75, Number 7 /July 1995
An analysis of the parents' responsiveness subscales identdied 17 "stable"
and 66 "responsive" children with
cerebral palsy. There were significant
changes in GMPM total scores for both
Table 8.
Cross Motor Performance Measure Mean Total Scores for '5table" and
"Responsive"Croups as Identijed by 7herapists and Parents
Time 1
Time 2
Change
Analysis of
Variance
F
X
SD
X
SD
X
SD
51.2
17.1
52.7
17.7
1.5
6.1
52.6
14.7
55.4
15.2
2.8
8.0
P,
ICC
2.13 1,35
,153
.36
12.30 1,59
,001'
.85
df
Therapist
Stable
(n=36)
Responsive
(n=60)
Fisher 2=4.4,P2<.00la
Parent
Stable
51.7
15.9
56.3
18.3
4.6
5.2
9.45 1,16
,007'
.81
52.4
14.1
54.7
15.9
2.8
6.5
8.97 1,65
,004'
.80
(n=17)
Responsive
(n=66)
Fisher 2=0.12,P2>.05
-
"Two-tailed probability, P,S.05.
the "stable" group (F=9.45; df=1,16;
P2=,0073) and the "responsive" group
(F=8.97; df= 1,65; P2=.0039). The
"stable" group appeared to experience
a greater change (4.6 units) than
the "responsive" group (2.8 units).
These data may indicate parents'
lower specific ability to judge overall
change in a construct such as motor
performance.
Intraclass correlation coefficients calculated from the F statistics in this
ANOVA showed a diference between
the therapist-identified "stable" and
"responsive" groups (P2<.001), but
not for the parent-identified groups
(P2>.05).
This responsiveness analysis demonstrates the ability of the GMPM to
detect change in motor performance
in children who have been judged by
trained therapists to be changing in
their overall quality of movement. This
capability is crucial for evaluative
instruments being used in clinical trials
of treatment effectiveness.
Discussion and Conclusions
There is sufficient evidence from this
study to satisfy a number of our original objectives in assessing the validity
34 / 610
and responsiveness of a measure of
quality of movement in a clinical setting. Attributes of gross motor performance can be defined, matched with
relevant gross motor function items,
and measured with a common scale.
A GMPM total score can be generated
that may be of use in describing overall motor performance.
An event could occur in assessment of
very young children or children with
severe disabilities, who cannot perform many motor function items,
which could have implications for the
interpretation of summary scores. The
use of percentage scores for individual
attributes may occasionally result in
attribute scores based on one or a few
observations. The contribution of this
score to the total score may outweigh
its overall importance to the construct
of motor performance. Analysis of
individual attribute data will allow us
to evaluate the impact of this issue
and subsequently to make necessary
changes to the GMPM scoring
procedures.
A limiting factor in this study was the
low statistical power to detect d&erences between certain subgroups.
Although we came close to enrolling a
satisfactory number of children in the
study, the number of children in the
age X severity groups was often too
low to allow us to be confident that
we avoided type I1 errors. This issue,
combined with the relatively small
effect size, or degree of change in
motor performance in children with
CP, could lead to an inability to detect
diferences even if they actually exist.
A small effect size may also have contributed to poor correlations between
GMPM change scores and parent/
therapist judgment ratings of change.
These problems require us to interpret
the data with some caution. Other
studies have reported similar problems
in comparing observational and biomechanical measures of motor performance in children with CP.22
Clinical hypotheses were supported
regarding the ability of the GMPM to
detect changes in movement quality in
children of diferent diagnostic and
severity groups. The observation that
major improvements in motor performance occurred in older children with
CP was unexpected. This pattern of
change in motor performance in the
older group contrasts sharply with
observed change in motor function in
a similar population. Russell et all0
reported that the greatest improvement in motor function in children
with CP occurred when the children
were young. The data from our study
tentatively indicated that the greatest
improvement in motor performance
occurred in both the 3- to 4-year-old
children with moderate CP and the
older children with moderate CP who
had presumably already acquired most
of their basic motor skills. These preliminary findings should be investigated further in longitudinal studies
with larger sample sizes. Other factors
that may contribute to d&erences in
motor quality, such as variations in
treatment frequency, should also be
controlled for in such studies.
Hypotheses regarding the relationship
between the GMFM and GMPM were
partially supported. Further analysis of
the data will allow us to explore the
critical relationship between function
and performance in d&erent severity
and age groups of children with CP.
Physical Therapy / Volume 75, Number 7 /July 1995
The hypothesis regarding the relationship between GMPM scores and therapist and parent ratings of change was
not well supported. The rating task
required of the parents and therapists
was to estimate the degree of overall
change in movement quality of the
child. There are several possible explanations for the low correlations
observed. The GMPM scores of children with CP changed very little over
the two assessments. Therapists' global
impressions of these changes may
have been influenced by concurrent
changes in function as well as by
changes in other aspects of motor
quality not assessed by the GMPM (eg,
speed of movement). In addition, a
change that was observed in a single
attribute on the GMPM may have
~nfluencedtherapist global ratings.
This change, however, may not have
been reflected in the total GMPM
score. Finally, because the GMPM
sampled a small number of the qualitative attributes of movement, it may
not have been realistic to expect that
overall judgments of movement quality by parents and therapists would be
correlated with GMPM change scores.
Thus, further refinement of the concepts and improved training of therapists in distinguishing between motor
function and performance may be
required.
The responsiveness analysis, however,
supported the use of the GMPM as a
measure for evaluating change in
motor performance. The initial analysis
indicated that the GMPM scores
changed in "responsive" groups of
children with CP and indicated that
when children are independently
classhed by therapists as either "stable" or "responsive," changes in the
GMPM accurately reflect these groupings. Nonetheless, this finding contrasts with the inability of the therapist
and parent rating scales to correlate
with GMPM change scores. Alternate
wording for "overall change in motor
performance" used in the rating scales
and the responsiveness subscale may
account for the observed findings.
This reinforces the conclusion that
further work is necessary before the
instrument's validity can be fully
established.
Physical Therapy / Volume 75, Numbe
We believe the GMPM represents an
important attempt to construct and
validate an observational measure of
quality of movement for use with
children with CP. Considerable conceptual, methodological, and practical
challenges have been partially overcome. Conceptually, there have been
advantages in utilizing an existing
measure of gross motor function as a
source of observable activities. There
are also difficulties, however, for observers to distinguish between motor
function and performance in scoring
activities.
terns of motor behavior in children
with CP.
Finally, there are many issues of theoretical importance to motor control
research that have been identified,
such as the relationships between
performance, function, age, and severity of impairment. There is also work
to be done on validation of the GMPM
with other kinematic measures of
motor performance and with other
populations of children with motor
performance impairments.
Acknowledgments
In practical terms, the need to simultaneously observe and rate three attributes of performance for each activity has proven a difficult task for
therapists. Those therapists who assessed numerous children reported
that this task became much easier with
experience. A number of these issues
must be resolved before the GMPM is
ready for use as a measure in a clinical
setting. At this time, the GMPM is
more suitable for research in controlled settings with well-trained
therapists.
Further study will be required to determine whether the evaluative properties of the GMPM, or its ability to
detect change over time, are as useful
as its discriminative properties, such as
its ability to discriminate between
different diagnostic, severity, and age
categories. The availability of a measure of movement quality would allow
a fuller assessment of gross motor
behaviors in children with CP. Treatments such as neurodevelopmental
therapy, use of "tone-reducing"anklefoot orthoses, and dorsal rhizotomy
may eventually be tested more completely with the GMFM and GMPM as
part of the evaluation protocol.
We are continuing to develop an
understanding of motor behavior in
children with CP. Future work in this
area may involve refinement of the
GMPM measure as a clinical tool and
evaluation of observer training techniques to ensure that potential users
are capable of learning and applying
this instrument to the complex pat-
We acknowledge the therapists, children, and parents who cooperated in
this study. Special thanks are extended
to the Children's Developmental Rehabilitation Program, Chedoke-McMaster
Hospitals; the Hugh MacMillan Rehabilitation Centre; and the Niagara Peninsula Children's Centre. Diane Tems
and Jim Chen assisted greatly with
data management and analysis.
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Appendix 1. Gross Motor Peformance Measure Attributes and 7beir Dejinitions
Alignment
The adjustment or amangement of parts or segments of the body in relation to each other.
Coordination
The smooth and controlled use of movements in motor performance. This takes into account
timing, velocity, direction, force, and amplitude.
Dissociated Movement
Isolated movement. Movement of one part of the body independent of another part (ie, one limb
independent of another limb, or one segment of the limb or trunk independent of another
segment). Movement that combines components of different motor patterns (eg, extension of
the hip with flexion of the knee).
Stability
The active maintenance of a body position in the presence of disturbing forces.
Weight Shift
Movement that involves a transfer of the body's center of gravity. This takes into account
amount and direction. The transference can take place in any of the four planes of the body
(posteriorly, laterally, anteriorly, and vertically) or any combination of these.
Physical Therapy / Volume 75, Number 7 /July 1995
Appendix 2.
Cms Motor Performance Measure Item Example
The child is positionedand asked or encouraged to complete an activity
Gross Motor Function Item
Sitting on mat with feet and small toy in front, child leans forward, touches toy, reerects without
arm propping
0. Does not lean forward and reerect
1. Leans forward but cannot reerect
2. Leans forward, touches toy, reerects with arm propping
3. Leans forward, touches toy, reerects without arm propping
During three repetitions of this activity, the therapist assesses and scores
Gross Motor Performance Attributes
Alignment of Trunk and Pelvis
1.
Severely malaligned the majority of the time; majority of movement is executed in the
extremes of range inappropriate to the performance of the task
2. Moderately malaligned the majority of the time
3. Mildly malaligned the majority of the time
4.
Demonstrates one trial with completely normal alignment and no evidence of movement
pathology
5. Consistently normal alignment for all three trials
Dissociated Movements of the Reaching Upper Extremity
1.
No dissociation the majority of the time
2. Moderate impairment of dissociation the majority of the time; absence of efficient movement
of one segment relative to another
3. Mild impairment of dissociation the majority of the time
4.
At least one trial with completely normal dissociation, with no evidence of movement
pathology
5.
Consistently normal dissociation for all three trials; efficient movement of one segment relative
to another within normal variations
Weight Shift
1. Severely abnormal weight shift the majority of the time; inappropriate position of center of
gravity; inappropriate direction of weight shift
2. Moderately abnormal weight shift the majority of the time
3. Mildly abnormal weight shift the majority of the time; weight shift always in the appropriate
direction
4. At least one trial with completely normal weight shift, with no evidence of movement
pathology
5. Consistently normal weight shift for all three trials
Physical Therapy / Volume 75, Number 7 /July 1995