Table 3.

Mediation analysis of the association between built environment and mental health measures in multivariable models.^a

Mediator	Direct effect (path E → O)	Indirect effect^b (path E → M → O)	Percent mediated^c
Distance → depression
Physical activity	−0.030 (−0.052, −0.008)^*	−0.001 (−0.004,0.003)	2.1%
Loneliness	−0.020 (−0.039, 0.000)^*	−0.012 (−0.020, −0.004)^*	40.7%
Social support	−0.029 (−0.051, −0.008)^*	−0.001 (−0.004,0.001)	3.5%
PM_2.5	−0.029 (−0.051, −0.006)^*	−0.002 (−0.003, 0.000)^*	5.5%
NO₂^d	−0.024 (−0.054, 0.006)	−0.001 (−0.004,0.001)	5.8%
Distance → anxiety
Physical activity	−0.016 (−0.031, −0.001)^*	0.000 (−0.001,0.001)	1.3%
Loneliness	−0.009 (−0.023,0.005)	−0.007 (−0.011, −0.002)^*	42.2%
Social support	−0.016 (−0.031, −0.001)^*	0.000 (−0.002, 0.001)	3.0%
PM_2.5	−0.015 (−0.030, 0.000)	−0.001 (−0.003,0.000)^*	8.7%
NO₂	−0.019 (−0.039, 0.001)	−0.002 (−0.004,0.000)^*	9.3%
Urbanicity → depression
Physical activity	0.228 (−0.054,0.509)	0.065 (0.021,0.109)^*	22.6%
Loneliness	0.127 (−0.128, 0.382)	0.193 (0.087, 0.300)^*	67.0%
Social support	0.245 (−0.038, 0.529)	0.046 (0.012, 0.080)^*	15.9%
PM_2.5	0.203 (−0.094,0.500)	0.084(0.007, 0.162)^*	29.4%
NO₂	0.133 (−0.238, 0.504)	0.049 (−0.023,0.122)	26.9%

All effects were expressed as the mean difference of the perceived stress per 50 m or interquartile range (57.8%) increment in distance to roadway or urbanicity, respectively.

Indirect effect was calculated as the product of two regression coefficients: (coefficient of exposure with mediator as the dependent variable) × (coefficient of mediator with mental health score as the dependent variable and exposure as another predictor).

Bold text refers to the statistically significant percent of mediation according to Sobel test (p_indirect < 0.05).

Mediation analysis treating nitrogen dioxide (NO₂) as mediator was restricted to a subset of NSHAP participants that resided within 90 km from a U.S. EPA ambient monitor that measured NO₂ concentrations.

p < 0.05.