| 年度 | 实际值 |
|---|---|
| 1993 | 26.6 |
| 1994 | |
| 1995 | 27.7 |
| 1996 | 28.2 |
| 1997 | 30.3 |
| 1998 | 30.9 |
| 1999 | 31.7 |
| 2000 | 34.4 |
| 2001 | 2.30666666666667 |
| 2002 | |
| 2003 | 30.62 |
| 2004 | 31.78 |
| 2005 | 33 |
| 2006 | 35.73 |
| 2007 | 37 |
| 2008 | 37.57 |
| 2009 | |
| 2010 | 39.7 |
| 2011 | 39.1 |
| 2012 | 39.31 |
| 2013 | 37.42 |
| 2014 | 36.89 |
| 2015 | 36.17 |
| 2016 | 37.43 |
| 2017 | 43.25 |
| 2018 | 41.44 |