Numerous studies conducted have found evidence for a positive relation between green space in peoples environment and self reported indicators of morbidity and mortality (Lee and Maheswaran, 2011). The authors in this study have found mortality from all causes to be higher in greener cities. Attempts have been made to adjust for factors which may act as confounders, however other community level factors have not been taken into account which influence mortality levels like health care access and crime rates in the cities. Part of the relation found in the study between green space and all causes mortality may be explained by indirect selection. Indirect selection takes place when people with certain characteristics related to well being (such as income) tend to live in a greener environment. Migration flows are related to sociodemographic characteristics such as age, income and education (Maas et al, 2009). Possible migration of the elderly post retirement to greener areas may most likely skew all cause mortality levels and which needs investigation. Moreover, no association was found between greenness and mortality from diseases of lung cancer, heart disease, diabetes and motor vehicle fatalities when analyzed individually. Analysis of the mortality data based on the city of residence may prove more helpful in understanding the association between greenness and health, given that many diseases develop temporally and exposure could have occurred in the past. Also, the authors have used the proportion of households without an automobile as a measure of automobile dependency for urban form and function. The number of household members and the number of cars per household have been ignored and which influence the measure of automobile dependency differently. References 1. Lee ACK and Maheswaran. The healthcare benefits of urban green spaces: a review of the evidence. J Public Health (2011) 33 (2); 212-222 2. Maas J, Verheij RA, Spreeuwenberg P, Groenewegen PP. Physical activity as a possible mechanism behind the relationship between green space and health: a multilevel analysis. BMC Public Health. 2008 Jun 10;8:206.

Conflict of Interest:

None declared