Table 4.

GAMM of the association between preceding amount of social activity and future sleepiness at different times of day

Variable	Estimate	SE	t-value	P value
Parametric coefficients
Intercept	−0.48	0.04	−12.88	<0.001
Workday	0.47	0.05	9.51	<0.001
Smooth terms	EDF	RefDF	F-value
Social activity [workday]	0.00	4	0	1.00
Social activity [freeday]	0.00	4	0	0.993
Time of day	2.97	3	472.20	<0.001
Social activity × time of day [workday]	4.83	12	13.94	<0.001
Social activity × time of day [freeday]	5.46	12	4.78	<0.001
Random intercept for participant	161.80	462	0.60	<0.001

GAMM, generalized additive mixed-effect model; EDF, effective degrees of freedom; RefDF, reference degrees of freedom. Smooth terms with categorical moderators, as specified in square brackets, represent separate smoothing terms given the moderator’s condition. An “x” between two variables represents a continuous interaction. All smooth terms are centered at zero. P values for smooth terms represent a test of whether the term is different to a flat line.