| 年度 | 实际值 |
|---|---|
| 1995 | 38.4 |
| 1996 | 39.5 |
| 1997 | 31.31 |
| 1998 | 38.5 |
| 1999 | 30.7 |
| 2000 | 22.9 |
| 2001 | 27.45 |
| 2002 | 29.17 |
| 2003 | 26.63 |
| 2004 | 26.74 |
| 2005 | 26.28 |
| 2006 | 25 |
| 2007 | 24.53 |
| 2008 | 22.68 |
| 2009 | |
| 2010 | 20.69 |
| 2011 | 20.99 |
| 2012 | 22.27 |
| 2013 | 21.78 |
| 2014 | 21.61 |
| 2015 | 25.81 |
| 2016 | 25.04 |
| 2017 | |
| 2018 | 21.22 |