- Correspondence to Dr José A Tapia Granados, Social Environment & Health Program/Survey Research Center, Institute for Social Research, University of Michigan, 426 Thompson Street, P.O. Box 1248, Ann Arbor, MI 48106-1248, USA;
- Accepted 21 November 2011
- Published in print 1 May 2012.
- Published online 2 April 2012.
- Published first 13 February 2012.
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