| 年度 | 实际值 |
|---|---|
| 1995 | 28.1 |
| 1996 | 27.9 |
| 1997 | 19.29 |
| 1998 | 22.2 |
| 1999 | 21.4 |
| 2000 | 24.1 |
| 2001 | 27.38 |
| 2002 | 28.2 |
| 2003 | 28.49 |
| 2004 | 28.18 |
| 2005 | 28.92 |
| 2006 | 21.95 |
| 2007 | 29.26 |
| 2008 | 29.61 |
| 2009 | |
| 2010 | 32.17 |
| 2011 | 31.49 |
| 2012 | 25.62 |
| 2013 | 25.15 |
| 2014 | 31.05 |
| 2015 | 28.18 |
| 2016 | 32.41 |
| 2017 | 30.49 |
| 2018 | 31.59 |