Taylor et al (2015) hypothesized that in areas with more trees, people who live there would have lower levels of depression. This study is one in a growing body of work on the effects of urbanization on citizens’ stress levels and how urban planning may improve their lives.
The study population is comprised of the people living in different areas of London. Exposure to nature was the independent variable and was operationalized as the number of trees on the street per kilometer. The lack of well-being was the dependent variable and was operationalized as the number of prescriptions for anti-depressants. The investigators used a correlational quantitative cross-sectional design to investigate the following hypothesis:
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number of prescriptions for anti-depressants = -f (number of street trees/km) + error
= -f (number of street trees/km) + (traffic + SES + ES + smoking + average age)
Possible sources of error identified in the study are (1) the variability of traffic along the streets within each area, and between areas, (2) the socio-economic status (SES) of the residents, (3) employment status (ES), (3) smoking rates and (4) average age. The first is important because according to the logic of urban planners, people must have “interaction” or contact with trees for them to exert their mood-enhancing effects. Thus, many trees in a street not accessible to citizens will have little impact. The rest are important as they independently correlate with depression.
The validity of using number of anti-depressant prescription as the outcome measure is debatable. Inability to cope with urban living may well manifest as depression but lack of depression does not necessarily mean happiness nor well-being. Secondly, anxiety and need for anti-anxiety drugs seem conceptually equally valid or even more so.
Notwithstanding these flaws, the study might still be useful as it offers a practical solution: keep people in cities but make sure the neighborhoods they live in and the streets they walk on have plenty of trees.
However, should the city adopt such a solution, we cannot be certain it would help the depressed citizens. Planting more trees in an area would improve its appearance which might in turn increase the cost of living there. Once made “greener” with more trees, increased costs might drive people from the area they call home, forcing them to areas with even more stressors.
Reference
Taylor, M.S., Wheeler, B.W., White, M.P., Economou, T., & Osborne, N.J. (2015). Research note: Urban street tree density and anti-depressant prescription rates--A cross-sectionl study in London, UK. Landscape and Urban Planning, 136, 174-179. doi:10.1016/j.landurbanplan.2014.12.005
