1390-4299 1390-4299 S1390-42992017000100008 10.17141/urvio.21.2017.3082 Ecuador 00 12 2017 00 12 2017 21 8 21

1993 12 (4) 12 (4) 361-81 2008 261-78 2013 2012 2011 2007 1999 2016 11-30. 1999 1999 2011 2011 2015 233-52 2015 21-38 2010 2004 23-48