Model statistics (R-squared, F-test and p-value), test statistics for an addition of trigonometric functions of months of birth (H0: A1 = A2 = 0), coefficients for the trigonometric functions, the amplitude and phase of trigonometric function of gross motor scores at 6, 10, and 14 months of age, and for differences between 6 and 10 months, and between 10 and 14 months of age.