Alberta Infant Motor Scale: Reliability and Validity When Used on Preterm Infants in Taiwan.

Infants born prematurely have a higher risk for developmental delays than full-term infants do, with motor delays accounting for the largest proportion of these problems,[1-3] Recent approaches to identifying and treating preterm infants with motor disorders have emphasized assessment and intervention within the first year of life.[4-6] Physical therapists are often the primary evaluators and care providers in the early identification and treatment of these children and are usually responsible for selecting an infant motor assessment that is clinically practical and psychometrically sound.

Physical therapists often relied on testing reflexes and motor milestones to evaluate infants with motor delays in the 1970s and 1980s.[7-12] These assessments were based on the concept that the behavior repertoire of an infant evolves from a reflexive state to a voluntary state in a sequential manner as the nervous system matures.[13] Although assessment of reflexes and motor milestones may provide useful information about the neurological integrity of an infant, increasing evidence indicates that the neural maturation explanation alone does not account for the complex features of motor development.[14,15] Rather, motor behaviors may emerge as a function of the cooperation of many contributing subsystems of the child in a task-specific context.[15-17] This notion, often referred to as "dynamical systems," suggests that assessment of infant motor behaviors should be based on multiple factors (eg, neural maturation, muscle force, biomechanical leverages, emotional state, cognitive awareness, constraints of the task and physical environment) that influence motor outcome.[18-21]

Another limitation of the traditional focus on acquisition of motor milestones is the lack of sensitivity in identifying children with subtle movement problems.[22,23] Several studies showing no benefits due to early neurodevelopmental therapy in premature infants used standard age-defined skill development levels.[4,24] The findings of those examinations indicated that the children did not exhibit acquisition of motor skills even though they may have shown clinical improvement in pattern and quality of movement. The scope of an infant motor test, therefore, should be broadened to include quality components (eg, ability to shift weight, posture assumed in the motor task, control of antigravity muscles) if the accuracy of early identification is to be improved.

The Alberta Infant Motor Scale (ALMS) incorporates the neuromaturational concept and the dynamical systems theory and is used to measure gross motor maturation of infants from birth through the age of independent walking.[25,26] In the AIMS, the impact of neurological components on motor development is reflected by a sequence of motor skills, which are used as the basis of assessment.[26] The scale follows the principles of dynamical systems because motor skills are tested by observing infants as they move into and out of 4 positions: prone, supine, sitting, and standing (Figure). In theory, this assessment should allow therapists to see the interplay of the child's neuromotor system within the specific physical contexts (eg, gravitational effect) of the motor task.

[Figure ILLUSTRATION OMITTED]

The items of the AIMS focus on variables such as weight bearing, postural alignment, and antigravity movement that contribute to motor skills.[26] This focus is exemplified by the description of the item "Supported Standing (3)" in Table 1. According to the scoring criteria, the infant needs to bear weight on his or her feet and maintain the head in midline, with the hips abducted and laterally (externally) rotated and in line with shoulders. This positioning assumes there is active control of the trunk and variable movements of the legs in order to get a passing score for this item. The scoring system entails a dichotomous choice for each test item, scored as "observed" or "not observed." Using criteria such as those in the example, the AIMS provides information that may assist therapists in identifying the missing components of motor tasks and formulating intervention strategies.

Table 1.

Contrast of Administration and Scoring Criteria for Comparable Test Items Among the Alberta Infant Motor Scale and the Bayley Motor Scale(a)

Test Item              "Supported Standing (3)"
Description            (Alberta Infant Motor Scale)

Administration         Stand the child on the
                         floor and support him or
                         her at chest level.
Key descriptors and    Weight bearing: Weight on feet.
  scoring criteria     Posture: Head in midline,
                         hips in line with
                         shoulders, and hips
                         abducted and laterally
                         (externally) rotated.
                       Antigravity: Active
                         control of trunk and variable
                         movements of legs:
                         may bounce up and
                         down, lift one leg, or
                         hyperextend the knees.
                       To pass this item, the infant
                         must have the heels
                         down at some point
                         during the observation
                         period and demonstrate spontaneous
                         movement in the legs.

Test Item              "Supports Weight Momentarily"
Description            (Bayley Motor Scale)

Administration         Stand the child on the floor and
                         hold his or her hands so that
                         the arms are extended at
                         shoulder height. If the
                         child appears able to support
                         his or her weight while
                         standing, slowly
                         loosen your hold on the child
                         according to his or her ability
                         to stand unsupported. Observe
                         the child to determine whether
                         he or she stands momentarily,
                         using your hands for balance
                         but not for support.
                       If the child stands momentarily
                         and supports his or her weight,
                         slowly remove your hands and
                         observe the child to determine
                         whether he or she stands alone.
                       Keep your hands close to the
                         child in case he or she loses
                         balance.
Key descriptors and    Give credit if the child supports
 scoring criteria        his or her own weight at least
                         momentarily (for at least 2
                         seconds), using your hands for
                         balance only.

"Adapted and reproduced with permission from Motor Assessment of the Developing Infant 26 and from Bayley Scales of Infant Development, 2nd ed.[12] (copyright [C] 1993 by The Psychological Corporation, a Harcourt Assessment Company, all rights reserved). "Bayley Scales of Infant Development" is a registered trademark of The Psychological Corporation.

The AIMS has been investigated for its practicality and the reliability and validity of its scores on infants in Canada[25-28] Because the testing procedures are administered by observation only and can be completed within 20 minutes, the AIMS is feasible for clinical use. Standardization of the scale was established on 2,202 sex- and age-stratified full-term infants who were randomly sampled from all infants in Alberta, Canada.[26] The normative data from this study provide the basis for determining whether the motor performance of normally developing infants differs from that of infants with motor dysfunction. Furthermore, the AIMS has high degrees of test-retest, intrarater, and interrater reliability when it is administered on normally developing full-term infants (reliability greater than .85).[26] The correlations between the AIMS and the established infant motor tests (ie, Bayley Motor Scale and Peabody Gross Motor Scale) are also high when these tests are concurrently applied on infants at risk for motor delays (Pearson product-moment correlation coefficients [r] greater than .80).[26] The prognostic value of the instrument in predicting the 18-month motor outcome of infants with very low birth weights (ie, [is less than] 1,501 g), however, ranges from moderate to high: the sensitivity was 58% to 64%, the specificity was 83% to 95%, and the positive predictive value was 49% to 79%.[27] Sensitivity was defined as the proportion of children diagnosed as having abnormal motor development during childhood who were also classified as having delayed motor development during infancy. Specificity was defined as the proportion of children diagnosed as having normal motor development during childhood who were also identified as having normal motor development during infancy. Positive predictive value was defined as the proportion of children classified as having delayed motor development during infancy who continued to have delayed motor development as they aged.

The theoretical basis, clinical feasibility, and, in our opinion, some acceptable psychometric test features of the AIMS have made it a valuable tool for the evaluation of high-risk infants in Canada. Before the AIMS can be applied more broadly, however, we believe a cross-cultural evaluation is warranted. Nugent et al[29] have illustrated that the psychometric properties of a developmental test might be influenced by some culture-specific elements. The AIMS test items are designed to evaluate an infant's movement in prone, supine, sitting, and standing positions. Previous studies[30-33] have shown that, unlike infants in North America, infants in Asia and Europe are predominantly placed in a supine position for sleeping, which has led to later attainment of what are considered early motor milestones, such as rolling over and sitting up. How such cultural differences might affect the administration of the AIMS has not been investigated. The AIMS incorporates a dynamical and qualitative perspective in the evaluation of infant movement, a framework that was recently formulated and is considerably new to therapists.[21,34,35] Application of the scale to different populations, in our view, is essential to verify the AIMS designers' contention that therapists with sufficient background in infant motor development, experience in infant observation, and understanding of the criteria for test items can make competent and accurate use of the AIMS.[36,37]

Estimates of reliability and validity for the AIMS have been made for use with Canadian subjects, but whether these estimates suggest that the AIMS is appropriate for infants of different social and ethnic backgrounds needs to be determined. The purpose of this study, therefore, was to investigate the reliability and criterion-related validity for the AIMS when used by physical therapists on preterm infants in Taiwan. The reliability studies examined intrarater and interrater reliability. The criterion-related validity studies were designed to examine whether the outcome of the AIMS could be used as a substitute for established tests (concurrent validity) and to predict subsequent developmental outcome (predictive validity).

Method

Subjects

Our subjects were 86 preterm infants who were followed at the outpatient clinic of the Pediatric Department at National Taiwan University Hospital, Taipei, from April 1995 through February 1996. All infants were considered at high risk for developmental delays because of prematurity or the presence of one or more of the following conditions: birth weight less than 1,501 g, 1- or 5-minute Apgar score lower than 7, intrauterine growth retardation, chronic lung disease, and intraventricular hemorrhage. Intrauterine growth retardation was defined as having a birth weight below the 10th percentile of the intrauterine growth curve of Taiwanese infants.[38] The presence of chronic lung disease was indicated if the child had continuous oxygen therapy at 28 days of age.[39] The severity of intraventricular hemorrhage was graded according to the method of Papile et al.[40] Informed parental consent was obtained for all infants prior to participation in the study.

The infants were subdivided into 2 samples, one to study the reliability of AIMS scores (n = 45) and one to study the validity of AIMS scores (n = 41). Table 2 illustrates the neonatal characteristics of each sample. In the reliability study, infants were evenly clustered into 3 age levels (ie, corrected ages of 0-3 months, 4-7 months, and 8 months or older) to ensure a fairly equal representation of different levels of motor performance from birth to age 18 months. The AIMS was administered to each infant once to investigate the reliability of the measurements obtained. All infants enrolled in the validity study had participated in one of our longitudinal follow-up research projects for infants with very low birth weights. The infants were evaluated with the AIMS and the Bayley Scales of Infant Development, 2nd edition, (BSID-II) at corrected ages of 6 and 12 months to investigate criterion-related validity. The Motor Scale of the BSID-II was used as the standard measure.[12]

Table 2. Characteristics of Subjects Included in the Reliability and Validity Studies(a)

                                 Reliability Study
Characteristic                   (n=45)

Male sex (%)                        60.0
Inborn (%)                          93.3
Gestational age (wk)                31.5 [+ or -] 3.0 (26-36)
Birth weight (g)                 1,523.4 [+ or -] 508.4 (686-2,906)
Intrauterine growth                 33.3
 retardation (%)
Apgar score
  1 min                              5.7 [+ or -] 2.3 (1-9)
  5 min                              7.9 [+ or -] 1.5 (4-10)
Intraventricular hemorrhage
 status (%)
  Grade I-II                        15.6
  Grade Ill-IV                       4.4
Chronic lung disease (%)            26.7
Duration of hospital stay (d)       61.6 [+ or -] 55.5 (2-265)

                                    Validity Study
Characteristic                      (n=41)

Male sex (%)                        51.2
Inborn (%)                         100.0
Gestational age (wk)                30.2 [+ or -] 2.8 (24-36)
Birth weight (g)                 1,135.8 [+ or -] 233.7 (630-1,500)
Intrauterine growth                 53.7
 retardation (%)
Apgar score
  1 min                              4.4 [+ or -] 2.7 (0-9)
  5 min                              7.1 [+ or -] 2.0 (1-10)
Intraventricular hemorrhage
 status (%)
  Grade I-II                        17.1
  Grade Ill-IV                       2.4
Chronic lung disease (%)            34.1
Duration of hospital stay (d)       64.1 [+ or -] 25.0 (30-122)

(a) The data are presented as the mean [+ or -] SD (range in parentheses) or percentage. "Inborn" indicates that the child was born at the National Taiwan University Hospital, compared with "outborn," indicating that the child was born at another hospital and was transferred to the National Taiwan University Hospital.

Instrument and Procedures

The AIMS consists of 58 items that are organized into 4 subscales: prone (21 items), supine (9 items), sitting (12 items), and standing (16 items).[26] For each test item, the examiner must identify and observe 3 key descriptors: weight bearing, posture, and antigravity movement. The content and key descriptors for each item have been described in detail.[26] The recently revised BSID-II contains the Motor Scale (111 items), the Mental Scale (178 items), and the Behavioral Rating Scale (30 items).[12] The instrument was normed on 1,700 infants, aged 1 through 42 months, and reliability and validity were established in the United States.[12] The interrater reliability for the BSID-II on full-term and preterm Taiwanese infants was established by our research team (percentage of agreement greater than .90). The content and criteria for each item are described in the manual.[12] The contrast of the administration and scoring criteria for comparable test items (ie, "Supported Standing [3]" versus "Supports Weight Momentarily") between the AIMS and the Bayley Motor Scale is presented in Table 1.

Six physical therapists (raters A, B, C, D, E, and F) served as the AIMS raters. The therapists had 3 to 5 years of experience in the evaluation and treatment of pediatric patients, but they had no prior experience in the administration of the AIMS. They undertook a 32-hour training course in understanding the theories of motor development and administration and scoring of the AIMS. The theories of motor development included the neuromaturational and dynamical systems theories. The section on administration and scoring of the AIMS provided instructions and demonstrations of the testing procedures and rating criteria of the scale. Following the training session, therapists were required to perform the AIMS on several normally developing full-term infants and preterm infants. All therapists' patient assessments were required to be in agreement with an experienced instructor's assessments on at least 90% of the items prior to study. Due to our training session and practice to achieve a level of agreement, our results may not reflect those obtained by therapists in general practice.

The data obtained for the infants examined during the training sessions were not included in the final analysis of reliability and validity. A psychologist who had 6 months of experience in the administration of the BSID-II served as the BSID-II rater. Her patient assessments agreed with an experienced psychologist's assessments on 90% of the items.

In the reliability study, the AIMS was administered to the infants by a physical therapist (rater A), and infant performance was videotaped by a videographer throughout the examination. To examine intrarater reliability, rater A scored the infant performance while administering the examination and rescored on the videotapes 1 month later. This time interval was considered long enough to minimize the memory bias of the rater. To examine interrater reliability, 2 physical therapists (raters B and C) observed the videotapes and independently scored the performance of the infants. Because of our use of a videotape, each rater did not have to handle the child. This eliminated one potential source of error. In general practice, differences in handling skills between therapists may lead to lower reliability.

In the validity study, the AIMS and the BSID-II were administered to the infants at corrected ages of 6 and 12 months. Both tests were conducted within 1 week of the infants' 6- and 12-month birthdays, with an interval of 1 to 7 days between tests. The AIMS was administered by 1 of the 6 physical therapists, and the BSID-II was administered by the psychologist. During the study period, no discussion was allowed between the physical therapists and the psychologist to ensure that the scorings of the 2 tests were independent and free from bias.

Data Analysis

Intrarater and interrater reliability were examined using the intraclass correlation coefficient (ICC) and the standard error of measurement (SEM). The ICC provides an estimate of the degree of agreement between observed test scores. It was derived from the random-effects analysis of variance models in which subjects and raters were treated as independent factors.[41,42] The SEM provides an estimate of the amount of error in an individual's observed test score. It was calculated as SD [square root of 1-r], where SD was the sample standard deviation and r was the correlation coefficient.[43]

The concurrent validity of the AIMS with the Bayley Motor Scale was determined by the correlation between the AIMS total scores and the Bayley Motor Scale raw scores at 6 and 12 months. The predictive validity of the AIMS scores was determined by the correlation between the 6-month AIMS total scores and the 12-month Bayley Motor Scale raw scores. The correlations were analyzed using Pearson product-moment correlation coefficients.

In our opinion, the levels of reliability described by Portney and Watkins[37] and the levels of validity described by Meyer[44] are accurate indicators of the extent of reliability and validity. The extent of reliability was determined as follows: correlation coefficients greater than .90 indicated high reliability, values between .75 and .90 indicated good reliability, values between .50 and .75 indicated moderate reliability, and values below .50 indicated poor reliability.[37] The extent of validity was determined as follows: correlation coefficients greater than .80 indicated high validity, values between .60 and .80 indicated good validity; values between .40 and .60 indicated moderate validity, and values below .40 indicated poor validity.[44] All statistical analyses were performed with the use of the Statistical Analysis Software program.(*)

Results

Intrarater and Interrater Reliability

The results of the intrarater reliability study for the 3 age groups are presented in Table 3. For the total scores, the SEMs between the first and second scores were less than 1.3 points, and the ICCs were greater than .95 across all age groups (P [is less than] .0001). For the subscale scores, the SEMs of the repeated scores were less than 0.9 point, and the ICCs ranged from .85 to .99 for all age groups (P [is less than] .0001). Of the 4 subscales, the correlation coefficients were the lowest for scores when the children were standing.

Table 4.

Scorings by Raters A, B, and C and Interrater Reliability as Determined by Standard Errors of Measurement (SEMs) and Intraclass Correlation Coefficients (ICCs)(a)

Age Group
and Subscale                Rater A                 Rater B

0-3 mo (n = 15)
  Prone                 2.9 [+ or -] 2.2       2.9 [+ or -] 1.8
  Supine                3.3 [+ or -] 0.7       3.1 [+ or -] 0.8
  Sitting               1.7 [+ or -] 1.1       1.9 [+ or -] 1.1
  Standing              1.7 [+ or -] 0.7       1.6 [+ or -] 0.5
  Total                 9.7 [+ or -] 4.0       9.5 [+ or -] 3.5

4-7 mo (n = 15)
  Prone                 9.7 [+ or -] 3.9       9.5 [+ or -] 3.5
  Supine                7.2 [+ or -] 2.0       7.3 [+ or -] 1.8
  Sitting               5.8 [+ or -] 2.3       5.4 [+ or -] 2.1
  Standing              2.9 [+ or -] 1.0       2.6 [+ or -] 0.8
  Total                25.6 [+ or -] 8.2      24.9 [+ or -] 7.3

8 mo or older
   (n=15)
  Prone                17.1 [+ or -] 5.5      16.9 [+ or -] 5.4
  Supine                8.5 [+ or -] 1.3       8.5 [+ or -] 1.3
  Sitting              10.1 [+ or -] 3.2      10.1 [+ or -] 3.1
  Standing              7.9 [+ or -] 4.1       7.5 [+ or -] 4.0
  Total                43.5 [+ or -] 13.1     43.1 [+ or -] 12.8

Age Group
and Subscale                 Rater C                SEM ICC

0-3 mo (n = 15)
  Prone                  2.9 [+ or -] 1.9           0.49 .94
  Supine                 3.3 [+ or -] 0.7           0.16 .93
  Sitting                1.9 [+ or -] 1.2           0.25 .95
  Standing               1.7 [+ or -] 0.5           0.31 .73
  Total                  9.7 [+ or -] 3.6           0.68 .97

4-7 mo (n = 15)
  Prone                  9.9 [+ or -] 3.5           0.71 .97
  Supine                 7.3 [+ or -] 1.8           0.40 .96
  Sitting                5.7 [+ or -] 2.3           0.47 .97
  Standing               2.7 [+ or -] 0.8           0.50 .75
  Total                 25.7 [+ or -] 7.6           1.24 .98

8 mo or older
   (n=15)
  Prone                 17.1 [+ or -] 5.2           0.05 .99
  Supine                 8.5 [+ or -] 1.3           0.01 .99
  Sitting               10.1 [+ or -] 3.0           0.44 .98
  Standing               7.9 [+ or -] 4.2           0.59 .98
  Total                 43.7 [+ or -] 12.7          0.13 .99

(a) The subscale and total scores are presented as the mean [+ or -] SD. The units for scorings and SEMs are points. All ICCs had probability values of less than .0001 ([F.sub.14,2]).

The independent scorings of the AIMS by raters A, B, and C and interrater reliability values for the 3 age groups are shown in Table 4. For the total scores, the SEMs between raters were less than 1.3 points, and the ICCs were greater than .95 across age groups (P [is less than] .0001). For the subscale scores, the SEMs between raters were less than 0.8 point for all age groups. Correlation analysis indicated ICCs for most subscales across age groups to be greater than .90 (P [is less than] .0001). The ICCs for the standing scores were .98 for infants 8 months of age or older (P [is less than] .0001), .73 in the 0- to 3-month-old group (P [is less than] .0001), and .75 in the 4- to 7-month-old group (P [is less than] .0001). The distributions of scorings by individual raters among the early standing items are presented for the 0- to 3-month-olds and the 4- to 7-month-olds in Table 5.

Table 5.

Distributions of Scorings by Raters A (First and Second Scorings), B, and C Among the Three Supported Standing Items in the 0- to 3-Month-Old Infants and the 4- to 7-Month-Old Infants

  Rater A

Age Group                      First    Second    Rater   Rater
and Test Item                 Scoring   Scoring     B       C

0-3 mo (n = 15)
  "Supported standing (1)"       7         6        6       5
  "Supported standing (2)"       7         7        9      10
  "Supported standing (3)"       1         2        0       0

4-7 mo (n = 15 [degrees])
  "Supported standing (1)"       0         0        0       0
  "Supported standing (2)"       6         5        8       6
  "Supported standing (3)"       8         9        6       8

(a) The standing performance of one infant was rated as "cruising without rotation."

Concurrent and Predictive Validity

Infants in the validity study achieved AIMS total scores ([bar]X [+ or -]SD) of 25.4 [+ or -] 4.9 and Bayley Motor Scale raw scores of 33.4 [+ or -] 4.9 at 6 months of age. At 12 months of age, they attained AIMS total scores of 49.7 [+ or -] 7.9 and Bayley Motor Scale raw scores of 58.0 [+ or -] 5.2.

Correlation analysis revealed a Pearson r of .78 between the 6-month AIMS total scores and the 6-month Bayley Motor Scale raw scores (P [is less than] .0001) and a Pearson r of .90 between the 12-month AIMS total scores and the 12-month Bayley Motor Scale raw scores (P [is less than] .0001). That is, the 6-month AIMS total scores and the 6-month Bayley Motor Scale raw scores shared about 61% ([r.sup.2] = .61) of the total variance, whereas the 12-month AIMS total scores and the 12-month Bayley Motor Scale raw scores shared about 81% ([r.sup.2] = .81) of the total variance.

The correlation (r) between the 6-month AIMS total scores and the 12-month Bayley Motor Scale raw scores was .56 (P [is less than] .001). There were correlations (r) of .51 between the 6- and 12-month scores within the AIMS (P [is less than] .001) and .53 within the Bayley Motor Scale (P [is less than] .001).

Discussion

Reliability

Our results, in our opinion, showed high levels of intrarater and interrater reliability (ICCs greater than .95) for the total scores of the AIMS when used on preterm infants from birth to age 18 months. The SEMs and reliability coefficients were similar to those reported for full-term Canadian infants.[26] The findings indicate that physical therapists in Taiwan, after a 32-hour training course in understanding the theories of motor development and administration and scoring of the AIMS, can reliably replicate their own and other therapists' assessments of preterm infants.

We compared the reliability values among the 4 subscale scorings in 3 age groups. The SEMs were small (less than 1.50 points) for all subscale scorings across age groups. The correlation coefficients were, in our view, high for most subscale scorings, except for those of the standing scores of the 0- to 3-month-olds and the 4- to 7-month-olds. The lower correlations of standing scores in the younger infants may be attributed to 2 factors: the small variability in test scores among the subjects and the difficulty in assessing early standing movements in infants.

The younger infants exhibited such a narrow range of scores that their standing performance was rated as "Supported Standing (1)," "Supported Standing (2)," or "Supported Standing (3)" on the scale. The ICC is defined as the ratio of the adjusted variance among the subjects to the sum of the variance among the subjects and error variance.[41] The small variability among the subjects for standing scores may thus attenuate the correlation coefficient values in the younger age groups.[42]

The difficulty in assessing the early standing movements in preterm infants may also contribute to the lower reliability for the standing scorings. According to the item descriptions of the AIMS, the major components for the acquisition of early standing movements are postural stability and mobility of the neck, trunk, shoulders, and lower extremities in various movement planes (Tab. 1).[26] Transitions from one standing movement to another (ie, from "Supported Standing [1]" to "Supported Standing [2]" and from "Supported Standing [2]" to "Supported Standing [3]") in a normally developing young child, therefore, require a high degree of coordination in those components.[45] The described scoring criteria, however, appeared to have limited sensitivity in detecting the subtle differences in the early standing movements of preterm infants in Taiwan. Future study is necessary to determine whether similar problems exist for the application of the AIMS on infants of different ethnicities.

Validity

Our results showed what we would consider good to high degrees of correlation between the AIMS scores and the Bayley Motor Scale scores when the 2 tests were concurrently applied on preterm infants. The correlation values were slightly lower than the data (r = .84 and .93) reported by Piper and Darrah.[26] The discrepancies may be due to sampling bias or methodological differences. Piper and Darrah[26] had the same assessor to perform the AIMS and the Bayley Motor Scale on infants, whereas we had different assessors administer the 2 tests on infants. In contrast to Piper and Darrah's study design, our study design eliminated the bias of the rater's temptation of giving similar ratings on the target and criterion tests, which may result in lower correlation values.[37]

The congruency between the AIMS scores and the Bayley Motor Scale scores was found to be stronger at 12 months than at 6 months. This difference may relate, in part, to the uneven distribution of gross and fine motor test items in the Bayley Motor Scale to adequately evaluate motor skills at all age levels in infancy. The Bayley Motor Scale consists of 91 gross motor test items and 20 fine motor test items.[12] There are 8 fine motor skill items for the 4- to 8-month age period, whereas there are only 4 fine motor skill items for the 10- to 14-month age period. The inclusion of primarily gross motor items in the Bayley Motor Scale at the 10- to 1 4-month age period may predispose Bayley Motor Scale scores to a high degree of correlation with AIMS scores, as the latter scale was constructed to assess gross motor behaviors.

The obtained congruency between the AIMS scores and the Bayley Motor Scale scores suggests that physical therapists may choose between the 2 scales to evaluate motor function of premature infants. The AIMS might better fulfill the current need in the field of infant motor assessment because the process and quality of movement as well as the achievement of specific milestones are considered. Furthermore, the ease of administration of the AIMS may make this instrument more feasible for use in follow-up clinics for infants at risk for motor delays.

The prognostic value of the 6-month AIMS scores in predicting the 12-month Bayley Motor Scale scores was only moderate. Our findings are consistent with the data established on the Canadian sample.[27] Limited predictive validity has also been documented for several infant motor tests, including the Movement Assessment of Infants,[46,47] the Bayley Motor Scale,[48-50] and the Peabody Developmental Motor Scales.[48] These results suggest that wide variability exists in the maturational course of motor ability in preterm infants during the first year of life.

Several factors may contribute to the instability in the early motor developmental scores of preterm infants. First, perinatal insults such as birth asphyxia,[51] intrauterine growth retardation,[52] intraventricular hemorrhage,[53] and chronic lung disease[54] can adversely affect neuromotor development. Recovery from these perinatal events, however, may be accompanied by rapid progress in neuromotor function, with concomitant improvement in motor scores.[46,55] Second, variations in the age of onset and the rate of resolution of transient neuromotor abnormality, which affects about 60% of infants with very low birth weights, may also add to the instability.[47,56-59] Finally, there is tremendous variability in the rates of neuromotor development among infants. Longitudinal follow-up studies of mental and motor development in infants at high risk for motor delays and in normally developing infants consistently show low to moderate degrees of stability in developmental scores.[28,46-50] Not only do the rates of development differ among infants, but there are also intraindividual variations in the rates of development at various times during childhood. Evidence from a twin study[60] suggests that the differences in the patterns of neuromotor progress among individuals may be determined to some extent by genetic factors.

Conclusion

The results of this study demonstrated high degrees of intrarater and interrater reliability for the AIMS when applied on preterm infants aged from birth to 18 months. Good to high degrees of concurrent validity were also found for the scale, using the Bayley Motor Scale as the criterion measure. The prognostic value of the AIMS was shown to be only moderate, however, in predicting the motor outcome of preterm infants at 1 year of age. Our results indicate that the AIMS provides reliable and valid measurements that can be used for the evaluation of the current motor function of preterm infants in Taiwan. Physical therapists should be cautious, however, in using the test scores at the earlier ages to predict later developmental outcome. The comparable estimates of reliability and criterion-related validity for the AIMS between the Taiwanese and Canadian samples suggest that the AIMS could be used cross-culturally for the evaluation of infant movement. Future study is needed to establish the normative data for the AIMS in Taiwan to provide the basis for discriminating motor function of normally developing infants from that of infants with motor delays. In addition, more work needs to be done on the issues related to predictive validity for the AIMS.

References

[1] Saigal S, Rosenbaum P, Stoskopf B, Milner R. Follow-up of infants 501 to 1,500 gm birth weight delivered to residents of a geographically defined region with perinatal intensive care facilities. J Pediatr. 1982; 100:606-613.

[2] Ungerer JA, Sigman M. Developmental lags in preterm infants from one to three years of age. Child Dev. 1983;54:1217-1228.

[3] Ross G. Use of the Bayley Scales to characterize abilities of premature infants. Child Dev. 1985;56:835-842.

[4] Goodman M, Rothberg AD, Houston-McMillan JE, et al. Effect of early neurodevelopmental therapy in normal and at-risk survivors of neonatal intensive care. Lancet. 1985;2:1327-1330.

[5] Resnick MB, Eyler FD, Nelson RM, et al. Developmental intervention for low birth weight infants: improved early developmental outcome. Pediatrics. 1987;80:68-74.

[6] Mayo NE. The effect of physical therapy for children with motor delay and cerebral palsy: a randomized clinical trial. Am J Phys Med Rehabil. 1991;70:258-267.

[7] Milani-Comparetti AM, Gidoni EA. Routine developmental examination in normal and retarded children. Dev Med Child Neurol. 1967;9: 631-638.

[8] Capute AJ, Accardo PJ, Vining EPG, et al. Primitive Reflex Profile. Baltimore, Md: University Park Press; 1978. Monographs in Developmental Pediatrics; vol 1.

[9] Chandler LS, Andrews MS, Swanson MW. Movement Assessment of Infants: A Manual. Rolling Bay, Wash: Chandler, Andrews, and Swanson; 1980.

[10] Folio MR, Fewell RR. Peabody Developmental Motor Scales and Activity Cards: A Manual. Allen, Tex: DLM Teaching Resources; 1983.

[11] Ellison PH, Horn JL, Browning CA. Construction of an Infant Neurological International Battery (INFANIB) for the assessment of neurological integrity in infancy. Phys Ther. 1985;65:1326-1331.

[12] Bayley N. Bayley Scales of Infant Development. 2nd ed. San Antonio, Tex: The Psychological Corporation; 1993.

[13] Heriza C. Motor development: traditional and contemporary theories. In: Contemporary Management of Motor Control Problems: Proceedings of the II STEP Conference. Alexandria, Va: Foundation for Physical Therapy; 1991:99-126.

[14] Thelen E, Fisher DM, Ridley-Johnson R. The relationship between physical growth and a newborn reflex. Inf Behav Dev. 1984;7:479-493.

[15] Thelen E, Ulrich BD. Hidden skills: a dynamic systems analysis of treadmill stepping during the first year. In: Monographs of the Society for Research in Child Development, Vol 56. Chicago, Ill: University of Chicago Press; 1991:23-35.

[16] Jeng SF, Holt KG, Fetters L, Certo C. Self-optimization of walking in non-disabled children and children with spastic hemiplegic cerebral palsy. Journal of Motor Behavior. 1996;28:15-27.

[17] Jeng SF, Liao HF, Lai JS, Hou JW. Optimization of walking in children. Med Sci Sports Exerc. 1997;29:370-376.

[18] Holt KG. Towards general principles for research and rehabilitation of disabled populations. Physical Therapy Practice. 1993;2 (4) :1-18.

[19] Jeng SF, Holt KG, Fetters L. A new approach to movement control in children with cerebral palsy: integration of dynamical systems and self-optimization. Physical Therapy Practice. 1993;2 (4) :19-29.

[20] Piper MC. Theoretical foundations for physical therapy assessment in early infancy. In: Wilhelm IJ, ed. Physical Therapy Assessment in Early Infancy. New York, NY: Churchill Livingstone Inc; 1993:1-12.

[21] Long TM, Tieman B. Review of two recently published measurement tools: the AIMS and the T.I.M.E.[TM] Pediatric Physical Therapy. Summer 1998;10:62-66.

[22] Harris SR, Heriza CB. Measuring infant movement: clinical and technological assessment techniques. Phys Ther. 1987;67:1877-1880.

[23] Stengel TJ. Assessing motor development in children. In: Campbell SK, ed. Pediatric Neurologic Physical Therapy. 2nd ed. New York, NY: Churchill Livingstone Inc; 1991:33-65. Clinics in Physical Therapy.

[24] Piper MC, Kunos VI, Willis DM, et al. Early physical therapy effects on the high-risk infant: a randomized controlled trial. Pediatrics. 1986;78:216-224.

[25] Piper MC, Pinnell LE, Darrah J, et al. Construction and validation of the Alberta Infant Motor Scale (AIMS). Can J Public Health. 1992;83 (suppl 2) :S46-S50.

[26] Piper MC, Darrah J. Motor Assessment of the Developing Infant. Philadelphia, Pa: WB Saunders Co; 1994.

[27] Darrah J, Piper M, Watt MJ. Assessment of gross motor skills of at-risk infants: predictive validity of the Alberta Infant Motor Scale. Dev Med Child Neurol. 1998;40:485-491.

[28] Darrah J, Redfern L, Maguire TO, et al. Intra-individual stability of rate of gross motor development in full-term infants. Early Hum Dev. 1998;52:169-179.

[29] Nugent JK, Lester BM, Brazelton TB. The Cultural Context of Infancy, Volume 1: Biology, Culture, and Infant Development. Norwood, NJ: Ablex; 1991.

[30] Bryant GM, Davies KJ, Newcombe RG. The Denver Developmental Screening Test: achievement of test items in the first year of life by Denver and Cardiff infants. Dev Med Child Neurol. 1974;16:475-484.

[31] Ueda R. Standardization of the Denver Developmental Screening Test on Tokyo children. Dev Med Child Neurol. 1978;20:647-656.

[32] Fung KP, Lau SP. Denver Developmental Screening Test: cultural variables [letter]. J Pediatr. 1985;106:343.

[33] Lira HC, Chan T, Yoong T. Standardisation and adaptation of the Denver Developmental Screening Test (DDST) and Denver II for use in Singapore children. Singapore Med J. 1994;35:156-160.

[34] Coster W. Critique of the Alberta Infant Motor Scale (AIMS). Physical & Occupational Therapy in Pediatrics. 1995;15:53-64.

[35] Case-Smith J. Analysis of current motor development theory and recently published infant motor assessments. Inf Young Child. 1996;9: 29-41.

[36] Rosenthal R, Rosnow RL. Essentials of Behavioral Research: Methods and Data Analysis. 2nd ed. New York, NY: McGraw-Hill Publishing Co; 1991:46-65.

[37] Portney LG, Watkins MP. Foundations of Clinical Research: Applications to Practice. East Norwalk, Conn: Appleton & Lange; 1993:53-67.

[38] Hsieh TT, Hsu JJ, Chen CJ, et al. Analysis of birth weight and gestational age in Taiwan. J Formos Med Assoc. 1991 ;90:382-387.

[39] Avery ME, Tooley WH, Keller JB, et al. Is chronic lung disease in low birth weight infants preventable? A survey of eight centers. Pediatrics. 1987;79:26-30.

[40] Papile LA, Burstein J, Burstein R, Koeffler H. Incidence and evolution of subependymal and intraventricular hemorrhage: a study of infants with birth weights less than 1,500 gm. J Pediatr. 1978;92: 529 -534.

[41] Shrout PE, Fleiss JL. Intraclass correlations: uses in assessing rater reliability. Psychol Bull. 1979;86:420-428.

[42] Lahey MA, Downey RG, Saal FE. Intraclass correlations: there's more there than meets the eye. Psychol Bull. 1983;93:586-595.

[43] Dudek FJ. The continuing misinterpretation of the standard error of measurement. Psychol Bull. 1979;86:335-337.

[44] Meyer CR. Measurement in Physical Education. New York, NY: Ronald Press Co; 1974:86-89.

[45] Bartlett D, Piper M. Mothers' difficulty in assessing the motor development of their infants born preterm: implications for intervention. Pediatric Physical Therapy. Summer 1994;6:55-59.

[46] Harris SR, Swanson MW, Andrews MS, et al. Predictive validity of the "Movement Assessment of Infants." J Dev Behav Pediatr. 1984;5:336-342.

[47] Coolman RB, Bennett FC, Sells CJ, et al. Neuromotor development of graduates of the neonatal intensive care unit: patterns encountered in the first two years of life. J Dev Behav Pediatr. 1985;6:327-333.

[48] Palisano RJ. Concurrent and predictive validities of the Bayley Motor Scale and the Peabody Developmental Motor Scales. Phys Ther. 1986;66:1714-1719.

[49] Crowe TK, Deitz JC, Bennett FC. The relationship between the Bayley Scales of Infant Development and preschool gross motor and cognitive performance. Am J Occup Ther. 1987;41:374-378.

[50] Coryell J, Provost B, Wilhelm IJ, Campbell SK. Stability of Bayley Motor Scale scores in the first year of life. Phys Ther. 1989;69:834-841.

[51] Bennett FC, Robinson NM, Sells CJ. Growth and development of infants weighing less than 800 grams at birth. Pediatrics. 1983;71:319-323.

[52] Allen MC. Developmental outcome and follow-up of the small for gestational age infant. Semin Perinatol. 1984;8:123-156.

[53] Vohr B, Ment LR. Intraventricular hemorrhage in the preterm infant. Early Hum Dev. 1996;44:1-16.

[54] Skidmore MD, Rivers A, Hack M. Increased risk of cerebral palsy among very low-birthweight infants with chronic lung disease. Dev Med Child Neurol. 1990;32:325-332.

[55] Wocadlo C, Rieger I. Developmental outcome at 12 months corrected age for infants born less than 30 weeks gestation: influence of reduced intrauterine and postnatal growth. Early Hum Dev. 1994;39:127-137.

[56] Drillien CM. Abnormal neurologic signs in the first year of life in low-birthweight infants: possible prognostic significance. Dev Med Child Neurol. 1972;14:575-584.

[57] Saint-Anne Dargassies S. Long-term neurological follow-up study of 286 truly premature infants, h neurological sequelae. Dev Med Child Neurol. 1977;19:462-478.

[58] Georgieff MK, Bernbaum JC, Hoffman-Williamson M, Daft A. Abnormal truncal muscle tone as a useful early marker for developmental delay in low birth weight infants. Pediatrics. 1986;77:659-663.

[59] Georgieff MK, Bernbaum JC. Abnormal shoulder girdle muscle tone in premature infants during their first 18 months of life. Pediatrics. 1986;77:664-669.

[60] Wilson RS, Harpring EB. Mental and motor development in infant twins. Dev Psychobiol. 1972;7:277-287.

SF Jeng, PT, ScD, is Associate Professor, School and Graduate Institute of Physical Therapy, College of Medicine, National Taiwan University, No. 7 Chun-Shan S Rd, Taipei, Taiwan ([e-mail]). Address all correspondence to Dr Jeng.

KIT Yau, MD, is Professor, Department of Pediatrics, College of Medicine, National Taiwan University.

LC Chen, PT, MS, is Teaching Assistant, School and Graduate Institute of Physical Therapy, College of Medicine, National Taiwan University.

SF Hsiao, PT, is a graduate student, School and Graduate Institute of Physical Therapy, College of Medicine, National Taiwan University.

Concept/research design, writing, and data analysis were provided by Suh-Fang Jeng; data collection, by Li-Chiou Chen and Shu-Fang Hsiao; and project management and fund procurement, by Suh-Fang Jeng and Kuo-Inn Tsou Yau. Subjects were provided by Kuo-Inn Tsou Yau, and consultation (including review of manuscript before submission) was provided by Kuo-Inn Tsou Yau and Li-Chiou Chen. Linda Fetters, PT, PhD, provided guidance during the early stage of this study, and Ru-Jeng Teng, MD, also provided consultation. Ru-Jeng Teng, MD, Ae-Wen Huang, PT, Chun-Hua Wang, PT, Cheng-Chi Tsao, PT, Yi-Lin Chang, Chia-San Wu, and Shiu-Ying Yu assisted in data collection and analysis. The authors acknowledge the infants and their parents for their participation in this experiment

This study was approved by the Institutional Review Committee of the College of Medicine, National Taiwan University.

This work was supported by a grant from the National Health Research Institute (NHRI DOH 87-HR-619) of the Department of Health and by the Premature Baby Foundation of the Republic of China on Taiwan.

This article was submitted March 22, 1999, and was accepted September 29, 1999.