J. Efird. International journal of environmental research and public health, 8 (1):
15-20(January 2011)6695<m:linebreak></m:linebreak>LR: 20110725; JID: 101238455; OID: NLM: PMC3037057; 2010/11/22 received; 2010/12/19 revised; 2010/12/21 accepted; 2010/12/23 epublish; ppublish;<m:linebreak></m:linebreak>Aleatorització; SAS.