| 年度 | 实际值 |
|---|---|
| 1995 | 32.6 |
| 1996 | 30.8 |
| 1997 | 27.1 |
| 1998 | 26.1 |
| 1999 | 23.3 |
| 2000 | 21.2 |
| 2001 | 20.13 |
| 2002 | 19.27 |
| 2003 | 18.52 |
| 2004 | 17.73 |
| 2005 | 18.26 |
| 2006 | 16.93 |
| 2007 | 16.46 |
| 2008 | 15.24 |
| 2009 | |
| 2010 | 15.65 |
| 2011 | 15.31 |
| 2012 | 15.69 |
| 2013 | 15.88 |
| 2014 | 16.6 |
| 2015 | 15.62 |
| 2016 | 13.65 |
| 2017 | |
| 2018 | 12.34 |