Saturday, June 9, 2012

Business districts and crime?

Beautiful patterns tell us how...not why

"When imagination sleeps, words are emptied of their meaning." Albert Camus  - 1960

Last blog discussed a study by US Forest Service researchers showing how tree canopy in Baltimore cut urban crime by 12%. I just read a 2010 study commissioned by the Center for Disease Control showing how business improvement districts cut violent crime by the same amount in Los Angeles.

So we cut crime 24% by planting tree canopies in a business improvement district (BID)?

Sounds silly. That's because both studies are correlational - studies that show a pattern between two things, not a cause. We don't know why canopies or BIDs work, only that they seem to have impact.

Dozens of correlational studies  appear each year. Like research showing underarm deodorant causes cancer. Or toothpaste. Or cell phones. Or smoking which, it turns out, is true. What to do?

There is a mantra in science: correlation-is-not-causation. Because there is a relationship doesn't mean you can infer cause. Tree canopy and BIDs may coincide with crime declines. That doesn't mean they cause them.

Unfortunately neither can we dismiss correlation studies. Doing so may result in dismissing a good cause assertion. The International Agency for Research on Cancer lists criteria for testing correlational studies - a plausible mechanism between cause and effect, a singular relationship between before/after effects, a reasonable time between the cause/effect, and so on. 

Satisfying these criteria helps mitigate the correlation-is-not-causation dilemma. 


I think what correlational studies need is simple - a plausible theory explaining why. That way we'll know if a study shows a correlational relationship we are seeing a shuffle not a full step. 

Sometimes I wonder if theory-building is a dead language. It shouldn't be! That's where research creativity and imagination really show up (not in clever data manipulation or new statistical methods). 

There are some great publications that provide imaginative theory, for example Gilligen's Preventing Violence and Kennedy's Don't Shoot".

It would be wonderful to produce a 24% cut in crime by planting tall trees with great canopy in a business improvement district. It would be a shame if they don't and we have no idea why.

5 Replies so far - Add your comment

Anonymous said...

Why do tree canopies work? I suggest a great book 'Healing Gardens: Therapeutic Benefits & Design Recommendations' by Clare Cooper Marcus & Marni Barnes, 1999. It has a list of some of the published research papers/publications about how just looking at a landscape of trees & grass physically lowers blood pressure & heart rate, decreases anxiety, sleeplessness, depression & pain levels, etc etc. The colour green is the most restful to the eye; a canopy offers protection from the elements, and provides a sense of safety; it creates a feeling of inclusion ('all-in-the-same-boat' feeling)among all who seek shelter under the canopy during a rainstorm...and people seem to respect an effort to landscape, to improve and bring nature back to a barren concrete jungle.
Cecilia Littleton, Landscape Designer.

GSaville said...

Thanks for that fascinating view Cecilia. I am a big fan of Clare Cooper Marcus's work. I will have a look at that book.

I do believe we need some coherent, and evidence-based, theory on this phenomenon. I have seen some of the research you mention, but it doesn't account for crime per se. For example, if green is restful and a canopy offers protection and a sense of safety, one might envision a well-landscaped and green painted suburban shopping mall satisfying those same human needs. That's not exactly a back to nature solution, but you take my meaning.

I'm being obvious, but we truly must have a clear sense of what theory it is we are building. If it is a matter of therapeutic gardens, that seems rather straightforward. I suspect the crime prevention reality may be more complex. It's a fascinating empirical question.

Thanks again for helping us along this important path.

Anonymous said...

While agreeing with your principle that “correlation is not causation” I have an interesting homicide I am working in Kansas City and am searching for materials that would support the contention that “spree” robberies (ie: armed robberies perpetrated by multiple assailants and in a 24 hour time period) are disproportionately likely to have the potential for escalating violence.

Anecdotal support from law enforcement confirms this belief- are you aware of any studies? Any thoughts or suggestions? Thanks


GSaville said...

Thanks JR. That's an interesting angle.

As far as I've read, that type of spree escalation has received very little research attention. I don't believe there is much conclusive evidence one way or another.

Intuitively it seems probable at least in a small number of extreme cases (psychopaths for example). I know there is some research on serial offenders (particularly murderers - Kim Rossmo's geographical profiling comes to mind). But not much else.

I know only of this study:

Hope it helps.

Justin said...

Very interesting correlation and I wonder why tree canopies make such a difference. I am thinking they must give business districts a feeling of peace and beauty versus the stark bleakness of just sidewalks, pavement and traffic.