From RSPB/Wildlife Trusts
Nature and Well Being Act Green Paper
The simple fact is that people tend to live longer when they have access to green space. Perceived neighbourhood greenness is strongly associated with better mental and physical health.44 Those living in highly green areas are much more likely to have better physical and mental health.45
44 Tanako, T., Nakamura, K. and Watanabar, M. (2002) Urban residential environments and senior citizens longevity in megacity areas: the importance of walkable green spaces. Journal of Epidemiology and Community Health 56: 913–918.
45 Sugiyama, T., Leslie, E., Giles-Corti, B. and Owen, N. (2008) Associations of neighbourhood greenness with physical and mental health: Do walking, social coherence and local social interaction explain the relationships? Journal of Epidemiology and Community Health 62: e9.
The research question is whether people who live longer live longer do so because of a causation with the environment or whether this is merely a correlation – specifically a spatial autocorrelation – that is their is a dependency on another independent factor and it is the non random distribution of this independent variable which is causing the spatial distribution.
A hypothetical example. People with poor mental health may find it difficult to afford a mortgage and so live in areas with less Green Space as these will be cheaper. This is not to say that the Green Space itself doesn’t affect health but you need to control for and test the independent influence of each.
Both of these studies only partially do this. They control for socio-economic variables but this is not enough. To give an extreme example- you might have a sample of equally well off people equally from Bombay (no open space) and Canberra (all open space) and conclude from that that the open space in Canberra makes people healthier, when living close to poorer people in poor health in Bombay may be the dominant cause. Unless you test for and model spatial autocorrelation you will never know.
Of course it is likely that Green Space makes you healthier. But this is a prior assertion. We need to know in public policy terms whether it is better in public health terms to spend 1 pound on health, Green spaceor welfare, and unless we carry out research properly into strength of causality we will never know the answer.
So please lets not use terms like ‘simple fact’ in documents with references, which gives a fuax impression of academic rigor when this is think tank like mere assertion. Unseemly when related to such a complex issue with complex causalities. This is illustrated in the second paper which found that
recreational walking was a significant predictor of physical health; however, the association between greenness and physical health became non-significant
In other words walking was the key and greeness doesn’t necessarily help if it is not accessible. There may therefore be other tested variables which effect walking, such as traffic congestion. which may be less in suburban areas which may be spatially autocorrelated with greenness. The paper cannot tell is what is the cause, lack of traffic congestion or greeness.