| 年度 | 实际值 |
|---|---|
| 1995 | 24.6 |
| 1996 | 25.1 |
| 1997 | 24.39 |
| 1998 | 23.1 |
| 1999 | 22.7 |
| 2000 | 21.3 |
| 2001 | 20.92 |
| 2002 | 20.23 |
| 2003 | 19.25 |
| 2004 | 20.97 |
| 2005 | 20.31 |
| 2006 | 18.12 |
| 2007 | 18.35 |
| 2008 | 16.87 |
| 2009 | |
| 2010 | 13.07 |
| 2011 | 12.69 |
| 2012 | 12.36 |
| 2013 | 11.92 |
| 2014 | 11.34 |
| 2015 | 11.19 |
| 2016 | 11.03 |
| 2017 | |
| 2018 | 10.77 |