| 年度 | 实际值 |
|---|---|
| 1995 | 28.4 |
| 1996 | 28.1 |
| 1997 | 29.23 |
| 1998 | 31.1 |
| 1999 | 32.2 |
| 2000 | 33.4 |
| 2001 | 26.06 |
| 2002 | 26.97 |
| 2003 | 28.92 |
| 2004 | 29.31 |
| 2005 | 28.11 |
| 2006 | 29.9 |
| 2007 | 30.55 |
| 2008 | 32.45 |
| 2009 | |
| 2010 | 38.23 |
| 2011 | 38.93 |
| 2012 | 38.71 |
| 2013 | 38.89 |
| 2014 | 38.16 |
| 2015 | 36.63 |
| 2016 | 35.53 |
| 2017 | |
| 2018 | 35.16 |