| 年度 | 实际值 |
|---|---|
| 1995 | 30.9 |
| 1996 | 31.2 |
| 1997 | 30.85 |
| 1998 | 30.8 |
| 1999 | 32.8 |
| 2000 | 31.9 |
| 2001 | 32.84 |
| 2002 | 32.94 |
| 2003 | 31.89 |
| 2004 | 30.78 |
| 2005 | 38.09 |
| 2006 | 38.63 |
| 2007 | 39.51 |
| 2008 | 38.52 |
| 2009 | |
| 2010 | 31.23 |
| 2011 | 29.8 |
| 2012 | 29.72 |
| 2013 | 32.61 |
| 2014 | 33.49 |
| 2015 | 36.53 |
| 2016 | 39.97 |
| 2017 | |
| 2018 | 39.7 |