Psychomotor developmental delay in the infant period could indicate a potential risk of the occurrence of developmental disorders in children (1). Early assessment of psychomotor development in infants allows for the recognition of delays, deficits, or disorders in its various areas, which enables the identification of infants in whom specialized neurodevelopmental diagnostics should be undertaken (2). The latest global recommendations concerning the detection of risk for neurodevelopmental disorders in young children (primarily cerebral palsy; CP) recommend supplementing basic diagnostics based on neuroimaging studies (primarily magnetic resonance imaging; MRI) with an assessment of infant motor development using validated and standardized developmental scales (3).

Currently, in clinical practice, several well-documented developmental classifications are used to detect psychomotor developmental disorders, such as: the Standardized Motor Assessment (MAI) and Alberta Infant Motor Scale (AIMS), Neuro Sensory Motor Development Assessment (NSMDA), Test of Infant Motor Performance (TIMP), Peabody Developmental Motor Scales (PDMS-GM), Hammersmith Infant Neurological Examination (HINE), Developmental Assessment of Young Children (DAYC), and Prechtl’s General Movements Assessment (GMA) (4).

A review of evidence-based research results regarding the prognostic value of diagnostic tools used for recognizing and predicting CP in newborns and infants demonstrated that for younger infants (i.e., those who have not yet reached 5 months of corrected age), the tools with the greatest capacity for detecting developmental risk are magnetic resonance imaging (MRI; sensitivity 86–89%), Prechtl Qualitative Assessment of General Movements (GMA; sensitivity 98%), and Hammersmith Infant Neurological Examination (HINE; sensitivity 90%). For older infants (i.e., those who have reached 5 months of corrected age), the most predictive tools for detecting developmental risk are magnetic resonance imaging combined with assessment using the Hammersmith Infant Neurological Examination (HINE) and Developmental Assessment of Young Children (DAYC). However, if performing an MRI on an infant is not safe or not feasible, diagnostics should be expanded with additional clinical diagnostics. For younger infants (i.e., up to 5 months of corrected age), conducting the Test of Infant Motor Performance (TIMP) is recommended, while for older infants (i.e., after 5 months of corrected age), conducting the Developmental Assessment of Young Children (DAYC) is advised. Additionally, in both cases it is recommended to conduct motor development assessment using the Alberta Infant Motor Scale (AIMS) or the Neuro Sensory Motor Development Assessment (NSMDA) (4).

Challenges in early recognition of motor developmental disorders in infants in our country (Poland) include both the small percentage of MRI examinations performed on children under two years of age, as well as the lack of tools for assessing motor development in young children that have been translated into Polish and culturally validated.

To address the problem of the lack of a validated tool for assessing child motor development, the TEST OF INFANTS’ DAILY LIVING ACTIVITIES (Test of IDLA) was developed on the initiative of the Polish professional self-government of physiotherapists (National Council of Physiotherapists, 1st term; KRF) by the Thematic Team for Quality and Monitoring of the Physiotherapy Process. The first version of the Test of IDLA was developed under the title “Guidelines of the National Council of Physiotherapists for functional assessment and medical documentation management for developmental age patients (0-7)” and was published in 2020 (5), while an update which consisted of minor specifications was introduced in 2023, and this development was included in a broader publication encompassing “Guidelines of the National Council of Physiotherapists for providing healthcare services in physiotherapy and their description in medical documentation” (6).

The TEST OF INFANTS’ DAILY LIVING ACTIVITIES (Test of IDLA) involves the observation and point assessment of spontaneous child activity in the following domains: (1) postural control (ability to assume and maintain specific positions); (2) motor control (gross motor skills); and observation combined with obtaining responses to questions posed to parents/caregivers of the child regarding: (3) dexterity (fine motor skills); and (4) self-care (social and emotional development), specifically defined and illustrated in appendices created expressly for this purpose. The assessment of spontaneous activity is conducted separately for children aged 0–24 months (part 1) and 2–7 years (part 2). Points are awarded according to the following criteria (5):

The measure of functional assessment here is the value of individual activity indicators (AI) determined in each domain (5, 6). The activity indicators are calculated based on the sum of points obtained in the examination and the child’s age, separately for children aged 0–24 months and 2–7 years, and separately for each domain. Areas of child development can therefore be assessed independently, so that examiners can evaluate only the domains that are of interest to them or test all four areas when measurement of general developmental level is desired, calculating the mean result from all domains.

The activity indicators for children aged 0–24 months - according to the following formula:

Each activity indicator reflects the current level of a child’s activity in a given area (activity indicator in a specific domain) or in terms of general developmental level (global activity indicator; mean value from 4 domains). This scale is constructed so that activity indicator values oscillate within the range 0–4. The higher the indicator value, the higher the child’s activity level. Interpretation of activity indicator AI: 0 ≤ AI<1 Very low; 1 ≤ AI<2 Low; 2 ≤ AI<3 Average; 3 ≤ AI≤4 High. The Test of IDLA was developed as a tool for observational assessment of spontaneous activity. The test begins with an observation and scoring of skills assigned to the child’s (appropriate) age range. Initially, skills from the completed month of life are assessed (in the case of children born before 37 weeks’ gestation, it is corrected age). For example, for a child who has turned 3 months but has not yet begun the 4th month, the appropriate skill range is “3 months of life” and their age in months is 3. The requirement for classifying the skills as adequate for the child’s age in each assessed area (domain) is obtaining the maximum number of points for each of the 2 specific skills, i.e., 4 points. Then each less mature skill from lower age ranges is assigned 2 points, i.e., a child aged 3 months who obtained 2 × 2 points for skills from the 3-month range is assigned 2 × 2 points for skills from the 2-month range and 2 × 2 from the 1-month range. Such a child obtains a total of 12 points in a given area, and their activity indicator equals 12 points ÷ 3 months = 4. In situations when a child, instead of obtaining the maximum number of points for age-adequate skills (4 points), obtains 3, 2, 1, or 0 points, we assess their skills in accordance with the requirements for lower maturity levels until obtaining the threshold condition, i.e., 2 × 2 points. Then we assign 2 × 2 points to each level below age and add to the point sum those obtained for skills from higher levels. For example, when a child aged 3 months obtains 1 point for each skill from the 3-month range (i.e., 2 points), and for skills from the 2-month level meets threshold conditions, i.e., 2 × 2, then their point sum equals: 4 points (for 2 months) + 4 points (2 × 2) assigned for 1 month + 2 points (2 × 1 for 3 months) = 10 points, their activity indicator is 10 points ÷ 3 months = 3.3. By design, the Test of IDLA does not assess skills from ranges above the child’s age.

Including the child’s current age in the activity indicator calculations allows for not only a quantifiable evaluation of the child’s activity level and a comparison of activity levels among children of different ages, but also precise tracking of changes in the child’s activity level over time, i.e., affected by physical and psychomotor development, disturbed CNS maturation, or applied neurodevelopmental therapy (Figure 1).

The Test of IDLA is a simple method for assessing child development, and conducting the assessment/evaluation in one area takes only several minutes. Its application in basic physiotherapy practice, both for functional assessment needs and physiotherapy documentation management, does not require any specialized training in this area. Individual skills have been listed on 4 purposely developed assessment cards and additionally explained in both publications listed above, in the form of photographic documentation. The IDLA scale is also available free of charge for every physiotherapist with the right to practice the profession, in the electronic FINEZJO application (https://app.finezjo.pl/logowanie), which significantly shortens assessment documentation time and enables obtaining various forms of graphic documentation, making it extremely appealing.

The research project, which aimed at (1) demonstrating construct validity of the IDLA scale; (2) demonstrating concurrent validity of the IDLA scale in relation to the Alberta Infant Motor Scale (AIMS); and (3) demonstrating predictive value of the Test of IDLA in psychomotor development assessment; as well as (4) repeatability and (5) reliability of IDLA assessment, was launched in 2023. The studies conducted within this work are part of the aforementioned project and concern construct validation of the Test of IDLA, i.e., assessment of psychomotor development in infants in the area of postural abilities (postural control domain) and motor skills (motor control domain) and are part of a broader research project.

The objective of the conducted studies was:

(1) to recognize the construct validity of the Test of IDLA; (2) to demonstrate the concurrent validity of the Test of IDLA in relation to the Alberta Infant Motor Scale (AIMS). The decision was made to conduct comparative studies relative to the AIMS scale as it is the most frequently used, normalized, translated into Polish, and culturally validated tool utilized for motor assessment of infants (7). Despite the very simple construction of the IDLA scale and the short time required to conduct the Test of IDLA compared to the very detailed and lengthy AIMS assessment, a research hypothesis was posed regarding a high correlation of Test of IDLA results in assessing the development of postural and motor control in infants with the results of motor development assessment in infants aged 0–18 months obtained using the AIMS scale.

The study obtained approval from the Thematic Team for Ethics in Scientific Research of Physiotherapists at the Polish Chamber of Physiotherapists by resolution dated June 29, 2022 (approval no. 15/52) and is consistent with the Declaration of Helsinki. The study was self-funded. Each parent was thoroughly informed about the study objectives, the nature of collected data, the inclusion and exclusion criteria, and received information about the possibility of withdrawing from the project, after which they expressed informed, written consent for their children’s participation in the research.

Construct and concurrent validity of IDLA in the domains of postural control and motor control in infants were assessed by comparing its results with AIMS scale assessment results, for accurate identification of developmental delays. The decision was made to conduct comparative validation of the postural assessment sheet and motor assessment sheet of the IDLA test, due to the fact that deficits in postural control and motor control are among the most frequently observed abnormalities in clinical physiotherapeutic practice and may significantly delay the process of reaching each consecutive stage in a child’s psychomotor development (15, 16).

The obtained results confirm high concordance between both scales (IDLA and AIMS) in classifying infants in terms of psychomotor development. This concordance is primarily determined by the high value of Spearman’s rank correlation coefficient = 0.72. Additionally, Cramér’s V = 0.78 and χ² (1, n = 357) = 217.518 indicate a very strong relationship between both scales. Based on this, it was determined that the Test of IDLA demonstrates validity and specificity at a sufficiently high level to recognize its psychometric properties in terms of construct validity as comparable to the psychometric values of the AIMS scale.

Spearman’s rank correlation values between 0.70–0.80 were obtained in validation studies of diagnostic tests AIMS, PDMS-2, TIMP, which indicates a strong monotonic relationship between test results, is significant for their reliability and diagnostic validity and demonstrates high concordance and utility in clinical practice (17–19).

Partial validation of the Test of IDLA, encompassing postural control (AI 1) and motor control (AI 2) modules, demonstrated extremely promising diagnostic properties of the instrument. The area under the ROC curve (AUC) of 0.928 (95% CI: 0.897–0.953) qualifies this instrument for the category of tests with “excellent diagnostic accuracy” (9). This value exceeds typical results obtained by recognized scales, such as AIMS (AUC 0.89–0.92) (19–22). This indicates that the Test of IDLA has substantial/immense potential in screening identification of neurodevelopmental disorders.

A fundamental stage in the construct and concurrent validity of the Test of IDLA was determining the optimal cutoff point. According to other studies, cut-off points are established and their effectiveness compared based on the ROC curve analysis, among other methods. The cutoff point represents an established threshold value of the result that allows for the classification of examined children into specific categories of normal development, or risk of developmental delays. This is performed in order to establish a practical interpretation of test results and assess its diagnostic properties (19, 23). According to reports by other authors, higher sensitivity and, consequently, lower cutoff points are preferred in screening studies so as not to overlook children at risk of neurodevelopmental delays, at the cost of a greater number of false positive results. In clinical diagnostics, the cutoff point may be more restrictive in order to limit the number of erroneous diagnoses (24–26).

In the study by Burger et al., the diagnostic value of the AIMS scale was compared with BSID-III (Bayley Scales of Infant Development-III) in children aged 6 months, and the predictive value of AIMS for motor delays at 18 months was assessed. After the ROC analysis, a new cutoff point was proposed that improved sensitivity to 63.6%, with acceptable specificity (81.6%) (27). Narrative and systematic reviews confirm that cutoff points are widely used in scientific research; however, their effectiveness may vary depending on population and child age (23, 28). In the work by Göthner et al., it was demonstrated that AIMS percentile values may not be fully transferable between different countries, which affects the effectiveness of cutoff points and emphasizes the need for local validation (28). Validation studies of the HINE scale suggest that different cutoff points have a high predictive value for diagnosing motor disorders and cerebral palsy, and their effectiveness has been confirmed in comparative analyses with MRI and other instruments (29, 30).

Cutoff points in infant motor scales (including BSID-II, BSID-III, AIMS, HINE, PDMS-2) have a proven predictive value, which has been confirmed in studies with control groups as well as using advanced statistical methods (31–33). Cross-sectional studies in various countries (including Norway and Greece) confirm the applicability of diagnostic scale cutoff points in assessing motor development in infants and indicate the necessity of considering population differences when interpreting results (28, 34).

In light of the above, determining the psychometric parameters of the Test of IDLA for the Polish population appears justified. The optimal cutoff point was established at the threshold of ≤3.22. On a 0–4 scale, it achieves a compromise between sensitivity (75.74%) and specificity (99.47%). Such configuration minimizes the risk of overdiagnosis in high-risk populations (35, 36). It is worth emphasizing that the adopted value of 3.22 is located in the upper part of the activity level according to the original IDLA classification, which requires revision of existing interpretive ranges.

An innovative approach to therapy monitoring, the IDLA – PM subscale, was proposed:AIPM=(AI1+AI2)2 And the following result interpretation (a positive result indicates that a psychomotor developmental delay was detected): 0.00 ≤ AI PM < 1.00: Very low (positive); 1.00 ≤ AI PM < 2.00: Low (positive); 2.00 ≤ AI PM < 3.00: Average (positive); 3.00 ≤ AI PM ≤ 3.22: Moderately high (positive); 3.22 < AI PM ≤ 4.00: High (negative).

The above proposal fills a significant gap in monitoring therapy progress in children classified below developmental norms. Unlike AIMS, which focuses on detecting deviations from patterns, IDLA–PM allows for monitoring of subtle changes in daily functioning, which is crucial for personalizing interventions in patients with psychomotor deficits. The AIPM indicator also enables measurement of the rate of functional improvement in infants with psychomotor developmental deficits undergoing therapeutic interventions. The instrument compensates for the lack of AIMS sensitivity in results classified as below norm, enabling precise tracking of effects of implemented physiotherapeutic interventions.

Based on achieved results and drawn conclusions, a comparative analysis between AIMS and IDLA (AI 1 & AI 2) scales was developed, and the IDLA–PM subscale was proposed (Table 10).

The IDLA–PM subscale focuses on two key domains (postural and motor control), allowing the creation of a specialized screening and therapeutic instrument. AIMS, conversely, does not allow tracking specific therapy progress in children with deficits, making it impossible to use as an instrument which conveys the information about therapeutic intervention progress.

IDLA–PM, as an instrument which meets the criteria for high diagnostic accuracy and low implementation cost, aligns with Lancet Commission on Diagnostics (37) recommendations regarding improving accessibility to early diagnosis of developmental disorders. Short test execution time (15–20 min) and applicability in primary healthcare conditions make IDLA–PM a particularly valuable instrument in healthcare systems, contributing to shortened functional diagnosis time, therapeutic pathway optimization, and improved long-term functional outcomes in at-risk children.

The study’s strength lies in its methodology and research sample. The study encompasses a relatively large sample of 357 infants aged 1 to 18 months, ensuring good statistical power (38). The demographic structure of the sample is well characterized and balanced in terms of gender (175 girls and 182 boys). The study followed a strict protocol described in Section 2.2, consistent with the approved ethical guidelines. The full study protocol is available at: https://doi.org/10.5281/zenodo.18605822. The study utilizes diverse statistical methods to assess psychometric properties of the Test of IDLA. A particularly strong element is the analysis of IDLA diagnostic properties: AUC value at 0.928 (95% CI: 0.897–0.953). This qualifies the instrument for the category of tests with “excellent diagnostic accuracy,” exceeding results of the recognized AIMS scale (AUC 0.89–0.92) (21). Due to the relatively large and gender-balanced sample, application of multiple different assessment methods, and the ROC curve analysis results, the study accurately reflects reality, and the drawn conclusions and analyses are supported by data.

A limitation of the study that should be considered and addressed in supplementary research is the partial validation of the Test of IDLA. The lack of data for dexterity and self-care domains prevents complete characterization of the neurodevelopmental profile, which may affect therapeutic decisions in cases of fine motor deficits and self-care difficulties. Therefore, validation of the complete Test of IDLA version, including all four modules, remains an important issue. Determining the reliability of the Test of IDLA also remains a crucial practical challenge. Another limitation of the present study is the absence of reliability data. However, reliability testing, along with the validation of the dexterity and self-care domains, is currently underway as part of the broader research project and will be reported in subsequent publications.

In summary, IDLA and IDLA-PM constitute an instrument of excellent diagnostic value and high clinical utility, particularly in monitoring therapy progress in infants with psychomotor developmental disorders. Preliminary construct and concurrent validity confirm the justification for its implementation in clinical practice, while simultaneously necessitating further validation studies on the complete test version.