| 年度 | 实际值 |
|---|---|
| 1995 | 30.2 |
| 1996 | 30.9 |
| 1997 | 31.52 |
| 1998 | 30.5 |
| 1999 | 29.2 |
| 2000 | 29.4 |
| 2001 | 29.38 |
| 2002 | 28.48 |
| 2003 | 27.79 |
| 2004 | 28.11 |
| 2005 | 29.66 |
| 2006 | 28.51 |
| 2007 | 28.65 |
| 2008 | 31.48 |
| 2009 | |
| 2010 | 30.34 |
| 2011 | 31.83 |
| 2012 | 32.69 |
| 2013 | 33.69 |
| 2014 | 37.97 |
| 2015 | 38.22 |
| 2016 | 36.23 |
| 2017 | |
| 2018 | 38.35 |