Table 12 Outcome variables and analysis methods

Eye-tracking

 - VOF task

Outcomes were percentage of detected stimuli, fastest reaction time, and average reaction time. The AOI consists of a circle with a 6 to 8 degree radius (depending on the size of the stimulus). A detailed description of criteria to determine if a stimulus was detected and to determine reaction time can be found in Kooiker et al. [16]. Participants were compared to typically developing children of their closest age (reference groups available until 12 years old) [16], and Z-scores were calculated

 - Social preference task

Outcomes were percentage of first looks (attention capture) and total looks (sustained attention) towards faces. To evaluate whether participants directed their first and total looks more often towards faces than would be expected by chance (20%), a one sample t-test was conducted. To identify fixations, identification by 2-means clustering was used, an algorithm built specifically for data across a wide range of noise levels [57]. Fixations were then assigned to an area of interest (AOI) using the Limited-Radius Voronoi Tessellation method [58] with a radius of four degrees

fNIRS

Oxy- and deoxygenated hemoglobin concentration changes were calculated. Signals were filtered to eliminate task-irrelevant systemic physiological oscillations. Data that were considered unusable (e.g., due to extreme motion) were excluded from analyses. The visual social condition was contrasted to the baseline, and the vocal condition was contrasted to the non-vocal condition. In this manner, the hemodynamic response was specific to the social stimuli, rather than visual or auditory stimulation per se

Indirect calorimetry

Resting metabolism rate (RMR) was predicted on the basis of height and weight [59]. The percentage difference between predicted and measured RMR was calculated. This difference was classified into slow, normal or fast metabolism

BIA and BOD POD

Percentage of body fat was used as outcome for both BIA and BOD POD and was classified into categories (underfat/normal/overfat/obese) using reference curves for children [38]. Lohman density model was used for BOD POD measurements

Body mass index (BMI)

BMI and BMI standard deviation score (SDS) were calculated using the pediatric formula of the Netherlands Organization for Applied Natural Science Research. BMI was categorized into underweight (≤ − 2 SDS), normal weight (> − 2 and < 1 SDS), overweight (≥ 1 SDS), or obese (≥ 2 SDS) using cut-off points determined by the World Health Organisation