| 年度 | 实际值 |
|---|---|
| 1995 | 28.1 |
| 1996 | 30.3 |
| 1997 | 29.68 |
| 1998 | 28.6 |
| 1999 | 31.2 |
| 2000 | 32.1 |
| 2001 | 32.44 |
| 2002 | 32.27 |
| 2003 | 30.7 |
| 2004 | 31.08 |
| 2005 | 31.94 |
| 2006 | 32.85 |
| 2007 | 36.07 |
| 2008 | 36.5 |
| 2009 | |
| 2010 | 35.51 |
| 2011 | 34.82 |
| 2012 | 35.64 |
| 2013 | 32.6 |
| 2014 | 36.98 |
| 2015 | 38.81 |
| 2016 | 39.83 |
| 2017 | 33.63 |
| 2018 | 34.35 |