Results of validation in the ARIMA (1, 1, 1) model
| Year | Actual values (‰) | Predictive values (‰) | 95% CI | Relative error (%) | |
| Upper | Lower | ||||
| 1992 | 15.57 | – | – | – | – |
| 1993 | 14.94 | 14.58 | 12.91 | 16.25 | −2.41 |
| 1994 | 12.77 | 13.76 | 12.50 | 15.03 | 7.75 |
| 1995 | 12.37 | 12.84 | 11.68 | 14.00 | 3.80 |
| 1996 | 11.55 | 11.69 | 10.57 | 12.80 | 1.21 |
| 1997 | 11.05 | 10.82 | 9.73 | 11.91 | −2.08 |
| 1998 | 9.66 | 9.98 | 8.91 | 11.05 | 3.31 |
| 1999 | 9.49 | 9.37 | 8.32 | 10.43 | −1.26 |
| 2000 | 7.76 | 8.51 | 7.47 | 9.56 | 9.66 |
| 2001 | 7.78 | 8.08 | 7.04 | 9.12 | 3.86 |
| 2002 | 7.10 | 7.22 | 6.18 | 8.25 | 1.69 |
| 2003 | 7.89 | 6.65 | 5.62 | 7.68 | −15.72 |
| 2004 | 5.47 | 5.80 | 4.77 | 6.82 | 6.03 |
| 2005 | 5.50 | 5.85 | 4.83 | 6.87 | 6.36 |
| 2006 | 5.76 | 5.21 | 4.19 | 6.22 | −9.55 |
| 2007 | 4.61 | 4.61 | 3.59 | 5.63 | 0 |
| 2008 | 4.41 | 4.46 | 3.44 | 5.47 | 1.13 |
| 2009 | 4.13 | 4.07 | 3.05 | 5.08 | −1.45 |
| 2010 | 4.16 | 3.76 | 2.75 | 4.77 | −9.62 |
| 2011 | 3.41 | 3.43 | 2.42 | 4.44 | 0.59 |
| 2012 | 3.29 | 3.37 | 2.36 | 4.38 | 2.43 |
| 2013 | 2.88 | 3.17 | 2.16 | 4.17 | 10.07 |
| 2014 | 2.89 | 3.10 | 2.09 | 4.10 | 7.27 |
| 2015 | 3.09 | 2.90 | 1.86 | 3.94 | −3.97 |