The data of Norwegian infants used in this cross-sectional study was extracted from a previous study on infant motor assessment (27). The inclusion criteria were infants aged 3–18 months, corrected for prematurity. The exclusion criteria were infants with severe medical conditions that precluded assessment, and those whose parents did not speak and understand Norwegian or English. Data from all infants aged 6–9 months were extracted for this study.

The sample was recruited from four municipalities in western and southeastern Norway; Porsgrunn, Bamble, Tønsberg, and Bergen, between October 2015 and June2020. Public health nurses assisted in recruiting all eligible parents or legal guardians of infants during regular checkups in well baby clinics. Participants were also recruited through word of mouth from former participants.

Detailed informed consent was provided to establish predictability and ensure that parents were fully aware of the study's aim, their role, and the handling of their data (27). The consent letter assured parents that they and the public health nurse would be notified of any concerns regarding the infant's motor function identified during the assessment. Parents were also informed, verbally and in writing, of their right to withdraw from the project at any time without affecting the follow-up service provided by the child healthcare centers. No participants withdrew from the study.

Scoring based on the Canadian AIMS norm reference was conducted in first half of 2023 using video recordings of assessments performed between October 2015 and June 2020 (27, 28). The third author (KMT), a specialist in pediatric physical therapy, conducted all assessments. Each infant was assessed once with minimal physical handling, ensuring they were in an alert, non-crying state. Various settings were chosen for conducting the assessments, including well baby clinics, the infant's home, the Western Norway University of Applied Sciences, and the Children's Physiotherapy Center in Bergen. Demographic characteristics of the sample and general population of Norwegian infants were obtained from the Medical Birth Registry of Norway (27, 29).

The main variables of interest in this study were the AIMS scores from the Canadian, Dutch, and Norwegian samples (9, 17). The AIMS assesses infants from term (40 weeks gestation) to 18 months post-term, based on observation of qualitative and functional aspects of spontaneous movement (9). Assessment is conducted using 58 observational items in the prone, supine, sitting, and standing positions. Each item is scored as 1 (observed) or 0 (not observed), with a total possible score of 58 points. Age-specific norms, adjusting for corrected age for preterm birth (before 37 weeks gestation), are used for identifying potential motor delays by applying cut-off percentiles. The cut-off for infants up to 8 months is the 10th percentile, and the 5th percentile is used from 8 months onwards (9). The AIMS is considered a cost and time-effective tool with robust psychometric properties (4, 9).

A previous study on the cross-cultural validation of the AIMS norms established a threshold for clinically significant differences as a variation of two points in the raw score (20). This threshold was also applied in this study.

Background characteristics of the Norwegian sample were analyzed using descriptive statistics. To determine the sample's representativeness of the Norwegian infant population, we compared it with open-access data from the Medical Birth Registry of Norway. The chi-square test was applied to assess differences in the categorical variables, while an independent t-test was utilized for the continuous variables. The sample distribution on the Canadian and Dutch AIMS percentiles was analyzed using descriptive statistics to calculate frequencies.

The total raw AIMS scores from the Canadian norms were compared to those of the Norwegian sample using an independent t-test for each age group, with a statistically significant level set at p < 0.05.

The same comparison with the Dutch norms was not possible because the total raw AIMS scores for the Dutch sample were not available (17). However, the Dutch material did provide a table of scores corresponding to each percentile in the norms, a format also available in the Canadian material (9). To facilitate comparison, we created a similar table for the Norwegian sample. This was done by sorting the infants by month and ranking them according to their AIMS scores, we determined the number of points required for the 5th–90th percentiles in the Norwegian sample.

Statistical analysis was performed using IBM SPSS Statistics (Version 29) and Microsoft Excel. Additionally, a medical statistician was consulted to ensure the robustness and validity of the statistical process employed.

This study utilizes previously collected data, where ethical approval was obtained from the Regional Committee for Medical and Health Research Ethics (2016/566 REK vest) and by the Norwegian Social Science Data Service (project no. 45014/3/MSS) (27). Informed consent was obtained from all parents or legal guardians involved.

Detailed characteristics of the sample, including information about infants and their mothers, are presented in Table 1. The sample comprises 189 infants, distributed across each age interval with a range of 44–51 infants per group. In the group of 9-month-old infants, there was a larger proportion of males, preterm infants, young mothers and variation of birth weight. None of the preterm infants were extremely preterm or had a very low birthweight (Table 1). They were thus considered low-risk infants.

No significant differences were found regarding infant sex, preterm birth status, or maternal marital status when comparing the sample characteristics to those of the Norwegian infant population. Significant differences in maternal age and parity were observed; our sample included a smaller percentage of mothers under the age of 25 and a higher percentage of first-time mothers. Additionally, the sample showed a significantly higher average birth weight than the general population. Overall, the sample was considered a low-risk group with demographics representative of the Norwegian infant population.

Figure 1 presents a tentative Norwegian percentile rank based on the scores of the sample. The Canadian norms consistently show the highest percentile ranks, followed by the Norwegian sample, and then the Dutch norms. The observed differences are considered clinically significant between Canadian and Norwegian norms, and Dutch and Norwegian norms. The Canadian norms are at least two points higher than the Norwegian ranks, with exceptions at the 5th percentile for ages 6, 8, and 9 months, and the 10th percentile for 7-month-old infants. Conversely, the Dutch norms are generally more than two points lower than the Norwegian ranks, except at the 90th percentile for infants aged 8 and 9 months.

Using Canadian norms, the median percentile rank for the Norwegian sample is the 50th, and the mean percentile value is 29.8. The Norwegian sample displays a left-skewed distribution with a higher prevalence of lower AIMS scores, as seen in Figure 2. Overall, 81% of the Norwegian sample scored at or below the 50th percentile, with 18% falling at or below the cut-off, indicating a possible motor delay. A substantial proportion of infants across all age groups scored at or below the 50th percentile: 94% at 6 months, 84% at 7 months, 70% at 8 months, and 77% at 9 months. Regarding cut-off scores, 30% at 6 months and 18% at 7 months scored below the 10th percentile. Additionally, 9% at 8 months and 16% at 9 months scored at or below the 5th percentile threshold.

Using Dutch norms, the median percentile rank is the 75th. This indicates a right-skewed distribution with a higher prevalence of higher AIMS scores (Figure 2). Overall, 20% of the Norwegian sample scored at or below the 50th percentile, with only 1% falling at or below the cut-off. Within each age group, a smaller proportion scored at or below the 50th percentile: 23% at 6 months, 22% at 7 months, 28% at 8 months, and 5% at 9 months. Regarding cut-off scores, none of the infants at 6 or 7 months scored below the 10th percentile. At 8 months, 2% fell below the 5th percentile, and at 9 months, no infants scored below this cut-off.

Figure 3 displays the comparison of the mean total raw AIMS scores between the Canadian normative sample and the Norwegian sample. There is a statistically significant difference across all age intervals with p-values below 0.001. The variation in mean total raw scores ranges from 4.1 to 5.6 points.

The sample size in our study was deemed adequate for a preliminary investigation into cross-cultural differences of the AIMS. It is estimated that a minimum of 20 infants per age group can provide 80% power for assessing the cross-cultural validity of the AIMS (35). Additionally, our sample size aligns with those of other studies that have studied the cross-cultural validity of the AIMS (20, 21, 36–39). The sample size was deemed too small to establish reliable percentile ranks (9, 40). Therefore, it is imperative to note that the Norwegian percentile values presented here are provisional and should be interpreted with caution when compared to Canadian and Dutch percentiles. The constrained sample size could potentially introduce bias into the comparison.

The sample was considered a low-risk group with demographics representative of the Norwegian infant population; however, additional examination is necessary. The study's scope was limited to two geographical areas and a few demographic variables. Hence, it is important to acknowledge that these may not encompass all the potential discrepancies between the sample and the broader population. Notably, influential factors such as socioeconomic background and health literacy were not accounted for in the analysis. The potential of self-selection bias ought to be considered, as participants in similar research in Norway tend to have higher socioeconomic background and enhanced health literacy (41–43).

Statistical considerations include the use of an independent samples t-test to compare AIMS mean total scores, despite the non-normal distribution of the Norwegian sample. The absence of necessary data for non-parametric tests within the AIMS material (9), necessitated the use of a parametric test for group comparison, which may be considered a study limitation. However, a Mann–Whitney U test was also conducted to compare the groups under the assumption that the Canadian values followed a perfectly normal distribution. This assumption introduces yet another potential limitation. Despite these methodological challenges, both tests indicated significant differences between the Canadian and Norwegian samples. After consulting with a medical statistician, we selected the independent samples t-test for its alignment with the methods used in other studies that have undertaken cross-cultural validation of the AIMS (14–16, 19, 20, 22, 35, 37, 44, 45). We consider this consistency in methodology as a strength of our research.

The stringent Canadian norms, currently used in Norway (5), may lead to the misclassification of normal motor development variations as delays. This could result in unnecessary referrals to pediatric physiotherapy and early intervention services, wasting resources and causing undue stress for families of healthy infants. Conversely, the more lenient Dutch norms might fail to identify infants with genuine delayed motor development among Norwegian infants. This could delay crucial early interventions, necessary service referrals, and the provision of adequate support to families truly in need.

These findings highlight the critical need for validated, culturally appropriate reference values for Norwegian infants to accurately evaluate motor development and prevent misclassification risks. Norwegian reference values should be generated from a large sample that accurately represents the proportion of preterm infants, socioeconomic background, and cultural diversity of the population (46). These considerations are key as these factors are known to influence infant motor development (4, 8, 13, 47–49).

In addition to creating a normative reference for the Norwegian population, it is important to recognize that language and cultural context significantly influence the validity of assessment tools (12). Cultural adaptations must extend beyond mere direct translation and should encompass a thorough translation process of the test manual conducted by a group of experts (50). Such a method ensure that cross-cultural adaptations are tailored to the specific context and are systematically validated, thereby contributing to more accurate assessments that can be reliably used in clinical practice (40).

In the absence of a Norwegian-adapted version of the AIMS, pediatric physiotherapists should cautiously interpret AIMS results, acknowledging that Norwegian infants may exhibit slower motor development compared to Canadian peers. It is important to recognize the limitations of standardized assessments, which might not capture an infant's complete motor skills, potentially leading to discrepancies in observed behaviors (4, 8). The AIMS should be considered one component of a comprehensive evaluation that includes clinical assessments, clinical reasoning, and critical evaluations (5).