| 年度 | 实际值 |
|---|---|
| 1993 | 19.6 |
| 1994 | |
| 1995 | 21.6 |
| 1996 | 32.3 |
| 1997 | 29.9 |
| 1998 | 29 |
| 1999 | 33.4 |
| 2000 | 34.3 |
| 2001 | 2.61333333333333 |
| 2002 | |
| 2003 | 27.97 |
| 2004 | 28.99 |
| 2005 | 31 |
| 2006 | 30.69 |
| 2007 | 33.79 |
| 2008 | |
| 2009 | |
| 2010 | 32.38 |
| 2011 | 28 |
| 2012 | 25.21 |
| 2013 | 25.19 |
| 2014 | 25.3 |
| 2015 | 25.67 |
| 2016 | 37.21 |
| 2017 | 36.81 |
| 2018 | 37.56 |