Confirmed injury prevention paper for #PHtwitJC 27

The winning paper in the poll for the 27th #PHtwitJC is:

GARVIN E, Cannuscio C, Branas C. (2013) Greening vacant lots to reduce violent crime: a randomised controlled trial. Inj Prev 19:198-203 doi:10.1136/injuryprev-2012-040439.

The full text can be accessed at this link:

The discussion will take place on twitter on Wednesday 31st July, at 8pm BST (GMT+1).

All are welcome to join the discussion at the Twitter Hashtag #PHTwitJC. If you have not joined a Twitter chat before, please see the ‘about’ tab above for some tips.


Green space can have a wide range of public health benefits, such as improving mental wellbeing and creating an area that are usable by the local community. Depending on the nature of the green space it can be used for play or exercise, leading to further benefits for the people and community who use it. From an aesthetic point of view, green spaces can be used to break up the monotony of urban environments and make it a lot more interesting and pretty!

The importance of green spaces is often reflected in policy too. For example, in England the use of outdoor spaces (including green spaces) is one of the public health outcomes indicators. Based on previous research, the specific role of green spaces in preventing violence is highlighted in ‘A public health approach to violence prevention for England’.

This study is the first randomised controlled trial that examined whether converting disused areas into green spaces can reduce violence.

Paper Summary:

The study used a Randomised Controlled Trial. 2,814 vacant lots were included in the study from a larger database of 54,132 vacant lots in Philadelphia in 2008. Lots in the same area were grouped together and then randomly assigned to receive ‘greening’ or to lie in their current state.

Vacant lots were ‘greened’ by the Pennsylvania Horticulture Society (PHS) in May 2011. The greening process was done to a standard where PHS; removed debris, improved the soil, planted grass and trees and built a low wooden fence with opening around the lot. The site was maintained the site every two weeks. There is a before-and-after image in the paper.

Reported crime – in the intervention area, 209 crimes were reported in the three and a half months before greening and 266 were reported during the same time period after. During the same time period at the control site, there was an increase in from 460 reported crimes before, to 521 crimes after. This meant that the unadjusted net difference-in-differences estimate was -4 at the greening site, which was a non-significant change (see table 2 for a break down of different types of crime).

Perceptions of disorder – A self-reported neighbourhood disorder scale was used to collect resident’s perceptions of disorder. An unadjusted difference-in-differences estimate was used again, and found that there was a reduction in perceptions of disorder at the intervention site compared with the control site. A regression-adjusted difference-in-differences estimate found that the differences were not significant.

The authors highlighted that a component of the perceptions of disorder scale that measures perceptions of safety found that this improved in the intervention site, and that this finding was highly significant when using both unadjusted and regression-adjusted difference-in-differences estimates.

The authors cocluded that the study ‘provides preliminary evidence that vacant lot greening may reduce violent crime and increase perceptions of safety’.

However, the authors also argued that larger trials would need to be conducted:

“Based on the findings of this smaller trial, these larger randomised trials will likely require hundreds of vacant lots in multiple study arms (greening intervention, trash pickup only and control) to have sufficient statistical power and detect meaningful effect sizes.”

It was suggested that this study provides a model for the larger trials.

Discussion Points:

1.Were the aims of this study clear? (consider whether it clearly defined the population, intervention, outcome and comparison)
2.Was the methodology appropriate? (for instance: were appropriate methods used to identify vacant lots, randomise the lot, and select local participants?)
3.Did the analysis use appropriate methods? (for instance: was the unadjusted difference-in-differences suitable for the comparisons)
4.Do you believe the results? The study reports non-significant reductions in crime and improvement in perceptions of disorder, but also a significant improvement in residents perceptions of safety, what could explain these findings? (for instance: chance, bias, or confounding?)
5.What implications do the findings have for public health practice & policy? (for instance: are the results applicable outside the US? What further research needs to be conducted?)

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1 Response to Confirmed injury prevention paper for #PHtwitJC 27

  1. Pingback: Summary of #PHTwitJC 27: ‘Greening vacant lots to reduce violent crime: a randomised controlled trial’ | Public Health Twitter Journal Club

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