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DEVELOPMENTAL MEDICINE & CHILD NEUROLOGY ORIGINAL ARTICLE
Have infant gross motor abilities changed in 20 years?
A re-evaluation of the Alberta Infant Motor Scale normative
values
JOHANNA DARRAH
1
|
DOREEN BARTLETT
2
|
THOMAS O MAGUIRE
3
|
WILLIAM R AVISON
4
|
THIERRY LACAZE-MASMONTEIL
5
1Department of Physical Therapy, Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, Alberta; 2School of Physical Therapy, Faculty of Health
Sciences, Western University, London, Ontario; 3Department of Educational Psychology, Faculty of Education, University of Alberta, Edmonton, Alberta; 4Department
of Sociology, Faculty of Social Sciences, Western University, London, Ontario; 5Department of Pediatrics, Faculty of Medicine, University of Ottawa, Ottawa, Ontario,
Canada.
Correspondence to Johanna Darrah at Department of Physical Therapy, Room 2-50 Corbett Hall, University of Alberta, Edmonton, Alberta T6G 2G4, Canada.
E-mail: johanna.darrah@ualberta.ca
This article is commented on by Vargus-Adams on pages 804–805 of this issue.
PUBLICATION DATA
Accepted for publication 9th February 2014.
Published online 29th March 2014.
ABBREVIATION
AIMS Alberta Infant Motor Scale
AIM To compare the original normative data of the Alberta Infant Motor Scale (AIMS)
(n=2202) collected 20 years ago with a contemporary sample of Canadian infants.
METHOD This was a cross-sectional cohort study of 650 Canadian infants (338 males, 312
females; mean age 30.9wks [SD 15.5], range 2wks–18mo) assessed once on the AIMS.
Assessments were stratified by age, and infants proportionally represented the ethnic
diversity of Canada. Logistic regression was used to place AIMS items on an age scale
representing the age at which 50% of the infants passed an item on the contemporary data
set and the original data set. Forty-three items met the criterion for stable regression results
in both data sets.
RESULTS The correlation coefficient between the age locations of items on the original and
contemporary data sets was 0.99. The mean age difference between item locations was
0.7 weeks. Age values from the original data set when converted to the contemporary scale
differed by less than 1 week.
INTERPRETATION The sequence and age at emergence of AIMS items has remained similar
over 20 years and current normative values remain valid. Concern that the ‘back to sleep’
campaign has influenced the age at emergence of gross motor abilities is not supported.
The Alberta Infant Motor Scale
1
(AIMS) is a Canadian,
norm-referenced measure to assess the gross motor abili-
ties of infants from birth to independent walking. Since its
publication in 1994, the AIMS has been used internation-
ally as a clinical
2,3
and research outcome measure,
4–8
and
as an educational resource.
9
The AIMS normative data
comprise 2202 infants born in Alberta, Canada, between
March 1990 and June 1992. The present re-evaluation of
the normative data was undertaken for three reasons.
First, the ‘back to sleep’ campaign initiated internationally
in the early 1990s
10,11
coincided with the AIMS normative
data collection, but many infants were not yet being
placed in the supine position for sleep. Subsequent con-
cern that the age at appearance of some infant gross
motor abilities may be later because of the introduction of
supine sleep position,
5,6,12,13
some reports in the literature
have suggested that the AIMS normative data were out-
dated and may identify infants with typical development as
delayed in their motor development.
6,14,15
The second
impetus for a re-evaluation of the normative data was the
changing ethnic diversity of Canadian infants; 16.2% of
the Canadian population are visible minorities, 3.8% of
Canadians have an Aboriginal background but only 10%
of the original AIMS normative sample had one of these
backgrounds. Finally, some authors have voiced concern
that the AIMS norms are not applicable to infants in their
country,
16
and it would be beneficial to provide them with
a feasible statistical method to compare their infants’
AIMS data with the normative data. The objective of
the study was to compare the original normative data
of the AIMS with a contemporary, representative sample
of Canadian infants.
METHOD
Design
A cross-sectional cohort study design was used. As far as
possible, the study design mirrored the design of the origi-
nal normative project.
©2014 The Authors. Developmental Medicine &Child Neurology published by John Wiley &Sons Ltd on behalf of Mac Keith Press. DOI: 10.1111/dmcn.12452 877
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and
distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
Participants
In the original normative study, the 58 AIMS items were
placed in one of three age groups representing their ages
of emergence: 22 weeks or less (19 items), 23 to 36 weeks
(19 items), and 37 weeks and older (20 items). For this
study, a sample of 450 infants (150 infants in each age cat-
egory) would produce a standard error equal to the largest
standard error in the original AIMS norms (1.3 points). To
ensure both the inclusion of infants representing visible
minorities (16.2%) and Aboriginal categories (3.8%) as
reported in the 2006 Canadian Census and the representa-
tion of gross motor variability,
17
an additional 75 infants
were added to each age category for a targeted sample size
of 675. Assuming a 25% attrition rate, the recruitment
target was 845 infants from six Canadian cities. Fifty-four
preterm infants (8%) were included in the recruitment
strategy to represent the prevalence rate of preterm births
in Canada.
18
For the original project, the Department of Vital Statis-
tics identified a random sample of potential participants,
but current confidentiality rules prevented similar identifi-
cation for the present study. Instead families were identi-
fied from the nurseries of hospitals in six Canadian cities
(Vancouver, Edmonton, Winnipeg, Toronto, Montreal,
Halifax) when their infants were born. In most centers,
study information letters were provided to all families and
the recruiting person, usually a nurse, met with the families
who wanted to know more about the study. Information
about families who wanted to participate was sent to one
of two project coordinators who then contacted the family
and discussed study specifics. Each infant was randomly
assigned an assessment age in one of the three age catego-
ries, using an age grid in weeks to ensure that ages in
weeks were uniformly represented in each of the three age
categories. Infants representing preterm, visible minority,
and Aboriginal subcategories were distributed among the
three age categories. The selection criteria for participation
were similar for both studies; all families interested in
participating were included in the study.
Data collection
Each infant had one AIMS assessment at an assigned
assessment age between 2 weeks and 18 months (adjusted
age was used for preterm infants). Two pediatric therapists
in each of the six cities attended a 1-day training session
led by JD and DB, who were assessors in the original nor-
mative project and who have both used the AIMS exten-
sively. At conclusion of the training, each therapist
observed and scored a video-recorded AIMS assessment.
Therapists had to achieve an 80% item agreement with
the criterion standard scoring criteria. During the 2 years
of data collection, therapists completed two more video-
scoring sessions. In addition, the therapists participated in
three teleconferences to discuss scoring and other adminis-
tration issues as the assessment ages changed, and a site
visit was made to each participating centre by either DB or
JD to observe each therapist completing assessments and
to address any specific site issues.
All assessments were completed at a clinical or academic
site. A therapist scored each item and provided general
information to the parent. The two project coordinators
calculated the total score and the centile rank for each assess-
ment using the centile graph on the AIMS score-sheet
(Fig. 1). The graph plots infants’ ages in months (horizontal
axis) and the total raw score (vertical axis) and provides
the 5th, 10th, 25th, 50th, 75th, and 90th centile ranks.
A centile rank score is derived by plotting an infant’s age
(to the closest week) against his or her total score, interpolat-
ing the centile rank if necessary. The project coordinators
designed a grid of centile ranks and ages to ensure that inter-
polation of centile rankings from the centile graph were the
same for infants of the same age with the same total score.
Data analyses
An important psychometric characteristic of the AIMS is
that items describing differing motor abilities can be placed
on the age scale representing the age when 50% of the
infants would pass each item. This is known as the item
location. Item locations can be calculated for each of the
two data sets. Comparison of the two sets of locations
makes it possible to see if the age scale shown in the origi-
nal norms
1
appears to have shifted. If the age scale has
changed, then the norms can be brought up to date by
adjusting the age scale.
There are four possible outcomes. (1) The item loca-
tions are the same in both data sets. This suggests that the
original norms are appropriate for interpreting the scores
of contemporary infants. (2) When plotted, the item loca-
tions for the two data sets fall on a straight line. The linear
relation between the two sets of locations tells us how the
current ages map onto the norming sample ages and
vice versa. New tables can be generated by applying a linear
transformation to the age values on the original tables.
(3) The order of the items is the same but the age difference
between items varies. A curvilinear transformation of the
original age scale is then necessary to generate new tables.
(4) The order of the items has changed, requiring a new
norming process with a larger sample.
This analytic strategy provides an efficient way to com-
pare data sets without recruiting a sample as large as the
original normative sample. We chose this method because
it can be replicated feasibly by other researchers who are
interested in comparing their data to the published AIMS
norms.
What this paper adds
•The current Alberta Infant Motor Scale (AIMS) normative values remain
appropriate to interpret an infant’s total AIMS score.
•Present infant gross motor abilities are similar to those documented
20 years ago.
•‘Back to sleep’ campaigns encouraging supine sleep positions have not
affected the age at emergence of gross motor abilities as measured by
AIMS items.
878 Developmental Medicine & Child Neurology 2014, 56: 877–881
To explore the four possibilities, a logistic regression
method was used to place AIMS items on the age scale for
each of the two occasions. The regression parameters were
rescaled to reflect the age at which 50% of the infants
passed the item. Details of the analyses are in Appendix SI
(online supporting information).
Ethical and administrative approval for the study was
obtained from the university ethics boards and health
centers.
RESULTS
Eight-hundred and sixty-eight families were recruited and
650 infants (338 males, 312 females) completed an assess-
ment. The sample included 15 (3.2%) infants with Aborigi-
nal heritage and 126 (19.4%) infants of visible minority.
Fifty-seven infants (8.7%) were preterm; 44 were 34
to 36 weeks’ gestation, and 13 were less than 34 weeks’
gestation.
Most mothers (588 [90%]) had post-secondary educa-
tion, 57 (9%) had completed high school, and five (1%)
had less than high school education. Five-hundred and
forty-seven families (84%) reported an annual family
income greater than $45 000. This income roughly repre-
sents Statistics Canada’s 2011 cut-off point for families of
four persons living above or below the low-income line.
The mean age of infants in the original sample was
37.4 weeks (SD 17.6, corrected for preterm birth if neces-
sary), older than the infants in the contemporary sample
(mean 30.9, SD 15.5wks). The age difference is primarily
because the contemporary sample was designed to have
proportionately more infants in the younger age regions
where most items are located. In addition, there was some
attrition in the contemporary sample that occurred with
infants in the oldest age category; many mothers had
returned to work and could not attend their appointments.
However, because the AIMS centile ranks ‘merge’ after
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 1960
55
50
45
40
35
30
AIMS score
25
20
15
10
5
0
5
th
10
th
25
th
50
th
75
th
90
th
Age (mo)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Figure 1: Alberta Infant Motor Scale (AIMS) centile ranks graph.
Normative Values of Alberta Infant Motor Scale Johanna Darrah et al. 879
14 months of age because of a scoring ceiling effect, the
impact of fewer infants at this older age is minimal.
Appendix SII (online supporting information) provides
the results of the regression and age location for all 58
items except for the four items whose regressions could
not be calculated. Ten more items were removed from the
next stage of analysis because they did not meet the stabil-
ity criterion that the proportion of infants passing the item
be between 0.10 and 0.90 in both data sets (the regressions
of age on performance are unstable for items that have
more than 90% of the infants passing or failing). One
additional item (Prone 21, mature creeping pattern) was
removed because of concern that it had been scored incor-
rectly. The 8-week age difference for this item between the
two data sets was the largest difference identified, and
closer examination of scores revealed that some therapists
had not scored this item for infants who were walking
independently.
The 43 remaining items were used for the next steps in
the analyses. Most of the items differed by 2 weeks or less
at the age when 50% of the infants passed the item and
the average age difference between item locations was
0.7 weeks (Table I). The correlation coefficient between
the two sets of age locations was 0.99, revealing a strong
linear trend. The original scale was mapped onto the con-
temporary scale using equation 3 (Appendix SI). Expressed
in months, the conversion equation is:
Xcontemp ¼1:001Xorig þ0:149:
Across the age scale from birth to 18 months, the maxi-
mum shift is less than one-sixth of a month (i.e. <1wk). In
other words, age values from the original data set when
converted to the contemporary scale differed by less than
1 week.
DISCUSSION
The results suggest that the current normative data of the
AIMS remain appropriate to interpret the results of an
AIMS assessment. The observed differences in the ages at
emergence of individual items between the original and
contemporary data are minimal and would affect neither
the research nor clinical decisions made using AIMS data.
Interpretation of an AIMS score is never made at the level
of individual items, but rather from the centile ranking
derived by plotting an infant’s age to the closest week and
his or her total score on the centile graph. The centile
rankings provided on the centile graph would be unaf-
fected for all infants because all age differences are less
than 1 week. Even if the centile ranks were moved over by
1 week of age, the clinical decisions would not change.
Previous work
17
suggests that infants do not maintain the
same centile score over time and that ‘windows of typical
development’ should be used rather than thinking that the
90th centile is ‘better’ than the 60th. Even centile ranks
near the recommended cut-off points to identify infants
with atypical development (10th centile at 4mo and 5th
centile at ≥8mo)
19
should not be used in isolation to make
clinical decisions regarding follow-up or intervention.
AIMS centile rank information should be incorporated
with other sources of information such as medical history,
other developmental aspects of an infant’s development,
and the family’s concerns to determine a clinical decision.
The age at emergence of gross motor milestones has
remained remarkably similar over 20 years. An analysis of
the age when 50% of infants passed the four rolling items
on the AIMS in the two data sets has been completed and
revealed that the items were very similar both in ages at
appearance and order of appearance.
20
Given the finding
that some items appear slightly earlier in the contemporary
data, the concern that the ‘back to sleep’ campaign has
resulted in delayed motor abilities appears to be
unfounded. It was not possible to collect information on
infant sleep position for all families, but 452 families
reported their infants’ sleeping position. Of these families,
304 (67.2%) placed their infants in supine, 46 (10.2%) used
a prone sleep position, 18 (4%) used a side position, and
84 (18.6%) used a combination of positions. The influence
that ‘tummy time’ while awake may have contributed to
the similarity of motor development over time cannot be
determined. No information was collected about the
amount of time infants played in prone during awake
periods, but anecdotally many parents reported that until
their infant could roll in both directions independently it
was challenging to keep their infant in prone for extended
periods of time while awake.
Some concern has been raised in the literature that
Canadian norms on the AIMS are inappropriate for infants
in other countries.
16,21
Our analyses approach may be
appealing to researchers interested in evaluating this issue
because it requires a smaller sample size than a norma-
tive project. The very small sample sizes reported by De
Kegel et al.
21
are worrisome and propose the need for new
normative data. Our analysis strategy is a feasible, cost-
effective strategy that can be replicated by other research-
ers. We are willing to share the original normative data
necessary for the comparisons. However, given the stability
of our results over a 20-year period and the increased eth-
nic diversity of the contemporary sample, it may not be
necessary to investigate international differences.
Table I: Agreement between item locations for 43 items used in
equation 3
Difference in
location
Number
of items
Item location
is earlier in
original data
Item location
is earlier in
contemporary data
<1wk 21 15 6
1–2wks 11 8 3
2–3wks 9 8 1
3–4wks 1 0 1
4–5wks 1 1 0
Total 43 32 11
880 Developmental Medicine & Child Neurology 2014, 56: 877–881
The AIMS profiles of infants of specific visible minori-
ties or gestational ages cannot be compared using these
data because of small subsample sizes.
CONCLUSION
The original centile ranks collected over 20 years ago con-
tinue to reflect the contemporary order and age at emer-
gence of infant motor abilities represented on the AIMS.
Clinicians can use the present AIMS centiles to interpret
both the research and clinical findings of an AIMS assess-
ment.
ACKNOWLEDGEMENTS
Canadian Institutes of Health Research Funding provided funding
for the project. The two project coordinators, Jamie Rishaug and
Jane Terhaerdt, were instrumental to the success of the study.
We thank the recruiters and assessors involved at each site.
Finally, we thank the infants and their families who allowed us
the privilege of observing the wonder of development once more.
Dr Johanna Darrah is the co-author of ‘Motor Assessment of the
Developing Infant’. (which contains the manual for the Alberta
Infant Motor Scale) and receives royalties for this text.
SUPPORTING INFORMATION
The following additional material may be found online:
Appendix S1: Details of regression analysis.
Appendix S2: Item locations for 58 items, original and
contemporary data sets.
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Normative Values of Alberta Infant Motor Scale Johanna Darrah et al. 881
