| 年度 | 实际值 |
|---|---|
| 1995 | 23.4 |
| 1996 | 23.9 |
| 1997 | 23.67 |
| 1998 | 23.6 |
| 1999 | 19.9 |
| 2000 | 21.5 |
| 2001 | 21.76 |
| 2002 | 20.9 |
| 2003 | 16.35 |
| 2004 | 17.14 |
| 2005 | 16.27 |
| 2006 | 14.76 |
| 2007 | 13.69 |
| 2008 | 13.82 |
| 2009 | |
| 2010 | 13.88 |
| 2011 | 14.32 |
| 2012 | 13.92 |
| 2013 | 13.15 |
| 2014 | 12.42 |
| 2015 | 11.86 |
| 2016 | 11.17 |
| 2017 | |
| 2018 | 9.91 |