| 年度 | 实际值 |
|---|---|
| 1995 | 29.8 |
| 1996 | 30.1 |
| 1997 | 34.25 |
| 1998 | 27.3 |
| 1999 | 30.4 |
| 2000 | 28.9 |
| 2001 | 28.29 |
| 2002 | 27.97 |
| 2003 | 31.36 |
| 2004 | 35.47 |
| 2005 | 32.41 |
| 2006 | 34.28 |
| 2007 | 34.13 |
| 2008 | 35.33 |
| 2009 | |
| 2010 | 40.35 |
| 2011 | 45.02 |
| 2012 | 45.02 |
| 2013 | 44.89 |
| 2014 | 44.39 |
| 2015 | 33.86 |
| 2016 | 32.72 |
| 2017 | 31.07 |
| 2018 | 29.9 |