Table 1.

Select characteristics of adult twins in the University of Washington Twin Registry, stratified by access to green space^*, 2008–2012

	Number (%)
Characteristic	NDVI <0.57 N=2061	NDVI ≥0.57 N=2277
Male	668 (32.4)	722 (31.7)
Age (years)†	38.7±16.4	39.7±17.1
White	1875 (91.0)	2111 (92.7)
Hispanic	107 (5.3)	69 (3.1)
Income
Less than $50 000	943 (46.9)	925 (42.0)
$50 000 or greater	1068 (53.1)	1279 (58.0)
Total MVPA (minutes/week)†	113.7±90.6	113.1±87.4
Total walking (minutes/week)†	89.0±101.1	87.4±101.9
Transit users	377 (18.3)	244 (10.8)
Singh Index†‡	−0.3 (0.8)	−0.4 (0.7)
Population density†	6294.8 (10 179.6)	2129.7 (2265.5)
Modified PHQ-2†	1.8±1.9	1.6±1.8
PSS†	13.5±6.8	13.2±6.8
BSI†	2.5±3.3	2.4±3.3

^*Access to green space assessed by the Normalised Difference Vegetation Index (NDVI), a measure of ‘greenness’ using satellites to assess the density of vegetation in the target area.

^†Mean±SD.

^‡Singh Index, a measure of neighbourhood deprivation which combines data on education, employment, income and income disparity, poverty, characteristics of the home and home, vehicle, and telephone ownership.

BSI, Brief Symptom Inventory, a measure of anxiety on a scale of 0–24; MVPA, moderate-vigorous physical activity; PHQ-2, 2-item Patient Health Questionnaire, a measure of depressive symptoms on a scale of 0–9; PSS, Perceived Stress scale, a measure of stress on a scale of 0–40.