| 年度 | 实际值 |
|---|---|
| 1995 | 27.2 |
| 1996 | 26.4 |
| 1997 | 38.84 |
| 1998 | 30.2 |
| 1999 | 32 |
| 2000 | 34.7 |
| 2001 | 34.37 |
| 2002 | 33.85 |
| 2003 | 31.9 |
| 2004 | 28.65 |
| 2005 | 31.97 |
| 2006 | 35.3 |
| 2007 | 33.53 |
| 2008 | 29.79 |
| 2009 | |
| 2010 | 28.85 |
| 2011 | 25.46 |
| 2012 | 26.25 |
| 2013 | 24.75 |
| 2014 | 29.9 |
| 2015 | 35.61 |
| 2016 | 36.88 |
| 2017 | 37.7 |
| 2018 | 40.06 |