Table 2.

Factor analysis, assuming three factors, of the 14 motion variables (numerical summaries of infant motor activity – see methods for details) that passed filters for missingness, reliability and redundancy

Item	Factor 1	Factor 2	Factor 3
Speed, N	0.90	0.08	0.03
Speed, RH	0.81	–0.05	–0.06
SD of 8 s block speed, N	0.72	–0.25	0.35
SD of 8 s block speed, RH	0.69	–0.18	0.16
Percentage time active, N	0.67	0.48	–0.42
Speed, LS	0.54	0.37	0.27
Speed periodicity (% p < 0.001, frequency < 1.2), RH	0.53	0.05	–0.06
Percentage time active, LH	–0.10	0.97	–0.07
Percentage time active, LE	0.03	0.94	0.02
Speed, LH	–0.06	0.72	0.38
Speed, LE	0.06	0.66	0.50
SD of 8 s block speed, LE	0.11	0.04	0.88
SD of 8 s block speed, LH	–0.06	0.13	0.80
SD of 8 s block speed, LS	0.55	–0.16	0.57

Factor loadings were estimated using the promax rotation from pairwise Pearson correlations between 179 subjects; 3% of data were missing; loadings exceeding ± 0.6 are shown in italic type