Temperament growth has been examined in infancy, but the spectrum of reactive and regulatory dimensions was not previously considered. We evaluated linear and nonlinear growth trajectories for overarching factors and fine-grained indicators of infant temperament obtained via parent report (N = 143) at 4, 6, 8, 10, and 12 months of age. Contributions of infant sex, family socioeconomic status, maternal stress, depression, and anxiety to trajectory parameters were also considered. Results indicated nonlinear trajectories as best fitting for negative emotionality (quadratic model) and regulatory capacity/orienting (piecewise), with a linear model deemed most optimal for positive affectivity/surgency. However, models of best fit associated with the overarching temperament factors were not consistently representative of the underlying fine-grained dimensions. Results indicate primarily nonlinear growth of infant temperament across the first year of life and support the importance of fine-grained level analyses. Effects of infant sex, socioeconomic status, maternal stress, anxiety and depression symptoms were generally consistent with hypotheses
