A study by David Hemenway from the Harvard Injury Control Resarch Center
Abstract:
http://ajl.sagepub.com/content/early/2011/02/01/1559827610396294.abstract
Full text:
http://ajl.sagepub.com/content/early/2011/02/01/1559827610396294.full.pdf+html
Abstract:
http://ajl.sagepub.com/content/early/2011/02/01/1559827610396294.abstract
Full text:
http://ajl.sagepub.com/content/early/2011/02/01/1559827610396294.full.pdf+html