| 年度 | 实际值 |
|---|---|
| 1995 | 28.8 |
| 1996 | 29.9 |
| 1997 | 32.9 |
| 1998 | 26.8 |
| 1999 | 28.2 |
| 2000 | 27.1 |
| 2001 | 26.92 |
| 2002 | 25.98 |
| 2003 | 21.86 |
| 2004 | 24.54 |
| 2005 | 19.7 |
| 2006 | 18.76 |
| 2007 | 18.84 |
| 2008 | 19.11 |
| 2009 | |
| 2010 | 18.67 |
| 2011 | 16.02 |
| 2012 | 14.9 |
| 2013 | 15.6 |
| 2014 | 13.55 |
| 2015 | 13.3 |
| 2016 | 12.82 |
| 2017 | 11.69 |
| 2018 | 10.54 |