| 年度 | 实际值 |
|---|---|
| 1995 | 28.7 |
| 1996 | 25.1 |
| 1997 | 22.17 |
| 1998 | 22.7 |
| 1999 | 23.9 |
| 2000 | 27.1 |
| 2001 | 27.12 |
| 2002 | 28.03 |
| 2003 | 28.38 |
| 2004 | 27.83 |
| 2005 | 19.9 |
| 2006 | 20.21 |
| 2007 | 20.84 |
| 2008 | 20.8 |
| 2009 | |
| 2010 | 26.13 |
| 2011 | 26.58 |
| 2012 | 25.81 |
| 2013 | 24.81 |
| 2014 | 22.81 |
| 2015 | 22.01 |
| 2016 | 21.48 |
| 2017 | |
| 2018 | 19.96 |