1390-6542 1390-6542 S1390-65422018000400120 10.29019/enfoqueute.v9n4.407 Ecuador 00 12 2018 00 12 2018 9 4 120 130

2015 1-5 1970 89 7 7 1670-8 2012 29 5 5 33-43 1983 130 5 5 237-44 2013 1970 89 1 1 120-5 2017 66 8 8 2036-45 University of Washington 1993 2011 5 1 1 29-37 (201 7 25 5 5