Abstract
The NIH Baby Toolbox® offers assessments spanning Cognition, Motor, and Social-Emotional Functioning domains and includes both measure-level and composite scores. Here, we describe the creation of eight composite scores, reflecting Language, Executive Function/Memory, Math, Cognition, Motor, Self-Regulation, Negative Affect, and Social Communication - key constructs in infant and toddler development. Using composite scores rather than measure-specific scores can offer a more holistic evaluation of functioning by combining measures, reducing the impact of outliers and measurement error. Using factor analysis, data from the original Baby Toolbox norming study (N = 2515 recruited; n = 2479 with at least one composite score; n = 2025 English, n = 454 Spanish) were analyzed to derive composite scores. Analyses were conducted on regression-weighted factor scores for individual measures to define composites. Psychometric properties were assessed using composite reliability, test-retest reliability, and external validation with the Ages and Stages Questionnaire (3rd edition), Bayley Scales of Infant and Toddler Development (4th edition), and the child's age. Composite scores demonstrated excellent composite reliability, moderate to strong test-retest reliability, minimal practice effects for most scores, moderate and significant relations with most external measures, and moderate to strong correlations with age for abilities expected to improve with age. The Baby Toolbox composite scores offer a reliable, valid tool for assessing key areas of infant and toddler development. The evidence supporting their reliability and validity demonstrates their effectiveness as indicators of early cognitive, motor, and social-emotional growth, making them useful in clinical, research, and educational settings. This framework helps deepen our understanding and practical evaluation of developmental milestones during the early years.