Actimetry in infant sleep research: an approach to facilitate comparability

STUDY OBJECTIVES: Only standardized objective assessments reliably capture the large variability of sleep behavior in infancy, which is the most pronounced throughout the human lifespan. This is important for clinical practice as well as basic research. Actimetry is a cost-efficient method to objectively estimate infant sleep/wake behavior from limb movements. Nevertheless, the standardization of actimetry-based sleep/wake measures is limited by two factors: the use of different computational approaches and the bias towards measuring only nighttime sleep—neglecting ~20 % of sleep infants obtain during daytime. Thus, we evaluate the comparability of two commonly used actimetry algorithms in infants and propose adjustments to increase comparability. METHODS: We used actimetry in 50 infants for 10 continuous days at ages 3, 6, and 12 months in a longitudinal approach. We analyzed the infants’ sleep/wake behaviors by applying two algorithms: Sadeh and Oakley/Respironics. We compared minute-by-minute agreement and Kappa between the two algorithms, as well as the algorithms with sleep/wake measures from a comprehensive 24-hour parent-reported diary. RESULTS: Agreement between uncorrected algorithms was moderate (77%–84%). By introducing a six-step adjustment, we increased agreement between algorithms (96%–97%) and with the diary. This decreased the difference in estimated sleep behaviors, e.g. Total Sleep Duration from 4.5 to 0.2 hours. CONCLUSIONS: These adjustments enhance comparability between infant actimetry studies and the inclusion of parent-reported diaries allows the integration of daytime sleep. Objectively assessed infant sleep that is comparable across different studies supports the establishment of normative developmental trajectories and clinical cutoffs.