| 年度 | 实际值 |
|---|---|
| 1995 | 24 |
| 1996 | 23.1 |
| 1997 | 23.55 |
| 1998 | 23.1 |
| 1999 | 22.9 |
| 2000 | 22.6 |
| 2001 | 22.54 |
| 2002 | 22.68 |
| 2003 | 23.49 |
| 2004 | 21.65 |
| 2005 | 19.79 |
| 2006 | 19.39 |
| 2007 | 19.39 |
| 2008 | 17.24 |
| 2009 | |
| 2010 | 17.53 |
| 2011 | 18.23 |
| 2012 | 19.22 |
| 2013 | 19.72 |
| 2014 | 24.7 |
| 2015 | 26.34 |
| 2016 | 27.12 |
| 2017 | |
| 2018 | 31.09 |