0121-7488 0121-7488 S0121-74882017000100021 Colombia Colombia 00 06 2017 00 06 2017 8 1 21 28

[1] 1988 1139-45 [2] 1992 48 48 951-9 [3] 1993 12 12 1589-603 [4] 1997 97-378 97-378 [5] 1973 86-91 [6] 1974 69 345 345 169-73 [7] 1976 38 3 3 290-5 [8] 2004 1-10 [9] R Development Core Team. R 2014 [10] 1999 55 55 13-22 [11] 1958 53 282 282 457-81 [12] 1967 831-53