In this study, we could control for elements like personality – which remains relatively stable over time – that may impact both on where people live and how happy are they are. The great thing about a longitudinal study is that, without measuring personality in any way, we can control for such factors.
Dr Mathew White
A few weeks ago, ScienceOmega.com
reported on the finding that well-maintained vegetation can suppress certain types of criminal activity in urban areas
. Research published today in the journal Psychological Science
reiterates the idea that greener surroundings, particularly in towns and cities, can have a significant impact on the way we think, feel and behave.
Led by Dr Mathew White, a lecturer in risk and health at the University of Exeter Medical School’s European Centre for Environment and Human Health (ECEHH), the new paper shows that people living in urban areas where there is access to green spaces such as parks and gardens experience greater wellbeing than those who do not. The study draws its conclusions from an analysis of data collected in a national survey from households in the United Kingdom between 1991 and 2008.
Dr White explained that, while several previous studies have looked at the association between the mental health and wellbeing of city and town dwellers and their proximity to green spaces, these have all been cross-sectional, looking at a large number of people at a single point in time.
"We cannot tell from those studies whether green space improves mental health or if people with better mental health – perhaps because they are richer or have more stable personalities – tend to move to greener areas," Dr White went on.
"Our analysis used panel data from more than 12,000 people, collected over an 18 year period. In this way we could compare mental health in years when respondents were living in a very green urban area, for example, to their mental health in years when they were living in a less green urban area."
Previous cross-sectional work has focused on mental distress – how anxious and depressed people are – but the study conducted by Dr White and colleagues including Dr Ian Alcock, Dr Benedict Wheeler, and Professor Michael Depledge was able to take a wider view.
"While we also looked at mental distress, we additionally analysed a positive indicator called ‘life satisfaction’," Dr White clarified. "We found that green space had an effect on both variables, even controlling for the other. In other words green space both reduces mental distress and increases wellbeing through different mechanisms."
The longitudinal nature of the research, which was based on annual survey responses, meant that Dr White and his colleagues were able to rule out changes in income, employment, marital status and physical health, unlike other studies using only cross-sectional data.
"There is evidence to show, for example, that wealthier people are more likely to live in greener areas because house prices are higher, while on the other hand it has been suggested that people with a history of mental health problems are more likely to live in urban areas," Dr White related.
"In this study, we could control for elements like personality – which remains relatively stable over time – that may impact both on where people live and how happy are they are. The great thing about a longitudinal study is that, without measuring personality in any way, we can control for such factors."
Even when the effects of each of these other factors had been accounted for, the results demonstrated a significant correlation between lower levels of mental distress and greater life satisfaction from urbanites living in greener localities. The increase in wellbeing was roughly equivalent to a third of the impact of being married rather than unmarried, or a tenth of the impact of being employed instead of unemployed. Dr White explained how it was possible to make this sort of comparison.
"The statistical technique we used, called a fixed effects analysis, simultaneously looks at a range of different ‘states’ by averaging wellbeing data for every year spent in a different state for each individual and taking the aggregate of these," he said. "These states include, for example, living in a high versus low green space area, being employed versus unemployed, or being married versus single. By comparing the co-efficients of these different comparisons in the same model we can estimate their relative effects."
Although the findings do not necessarily establish that moving to greener pastures, as it were, will inevitably result in greater happiness, they do fit in with the knowledge planners have held for some time that there is an association between a lack of green space and mental ill-being. It was previously unclear, however, whether this was due to third-factor explanations such as personality or whether the same pattern held true for mental wellbeing.
"Neither were we aware of the extent of the effect that more green space can have in comparison to other factors that might change, like marital status," continued Dr White. "Our findings help provide more robust estimates of the relative importance of green space to other domains of life that might be influenced by policymakers."
Even short periods of time in green surroundings can improve mood and cognitive function, experimental studies have shown. The combined effect on the population of towns and cities may be of greater consequence than the relatively modest impact on the individual. In terms of further research, the ECEHH researchers currently have a paper on the link between coastal proximity and wellbeing, in which green space is controlled for, undergoing revisions.
"We are looking at a range of issues including the quality of green spaces in the areas that people move to and from, as well as simply the prevalence of green spaces, as in this research," concluded Dr White.