| 年度 | 实际值 |
|---|---|
| 1995 | 29.6 |
| 1996 | 26 |
| 1997 | 17.2 |
| 1998 | 24.7 |
| 1999 | 25.5 |
| 2000 | 25.9 |
| 2001 | 27.65 |
| 2002 | 30.22 |
| 2003 | 33.25 |
| 2004 | 32.6 |
| 2005 | 27.59 |
| 2006 | 29.17 |
| 2007 | 28.23 |
| 2008 | 25.56 |
| 2009 | |
| 2010 | 24.47 |
| 2011 | 24.94 |
| 2012 | 24.63 |
| 2013 | 23.99 |
| 2014 | 19.92 |
| 2015 | 19.25 |
| 2016 | 18.57 |
| 2017 | 18.14 |
| 2018 | 18.27 |