| 年度 | 实际值 |
|---|---|
| 1995 | 37.9 |
| 1996 | 36.2 |
| 1997 | 35.52 |
| 1998 | 32.2 |
| 1999 | 31.7 |
| 2000 | 33.9 |
| 2001 | 33.19 |
| 2002 | 32.82 |
| 2003 | 31.43 |
| 2004 | 29.61 |
| 2005 | 35.76 |
| 2006 | 33.25 |
| 2007 | 27.51 |
| 2008 | 27.35 |
| 2009 | |
| 2010 | 25.12 |
| 2011 | 24.87 |
| 2012 | 23.9 |
| 2013 | 22.46 |
| 2014 | 21.13 |
| 2015 | 20.91 |
| 2016 | 20.16 |
| 2017 | |
| 2018 | 18.23 |