Table 1.

Estimating the change in cortisol by duration of the nature experience (NE duration in hours), after accounting for the natural diurnal effect (time of day).

Effect	dfA	Beta	Standard error	p-value	% Cortisol decrease per hourB
Intercept		–0.542	0.1952	0.0064
Time of day (diurnal effect)	109	–0.124	0.01179	<0.0001	11.7%
Length of NE (NE duration)	128	–0.239	0.05815	<0.0001	21.3%

^ADenominator degrees of freedom ^BCalculated as e ^{beta estimate} – 1. The diurnal effect is expressed as percent change per hour of log cortisol. Linear mixed models were used to account for multiple NEs per person (36 subjects, n = 220 saliva samples from 110 NEs). This model explains 26.9% of level-1 (residual – repeated measure) variance, 47.9% of level-2 (subject-level) variance, and 53.7% of level-3 (timepoint-level) variance.