| 年度 | 实际值 |
|---|---|
| 1995 | 23 |
| 1996 | 23.4 |
| 1997 | 26.41 |
| 1998 | 27.7 |
| 1999 | 28.8 |
| 2000 | 28.9 |
| 2001 | 29.6 |
| 2002 | 30.01 |
| 2003 | 28.57 |
| 2004 | 26.24 |
| 2005 | 23.13 |
| 2006 | 23.37 |
| 2007 | 23.77 |
| 2008 | 21.76 |
| 2009 | |
| 2010 | 18.26 |
| 2011 | 18.08 |
| 2012 | 18.88 |
| 2013 | 18.46 |
| 2014 | 23.33 |
| 2015 | 26.09 |
| 2016 | 26.76 |
| 2017 | |
| 2018 | 29.72 |