| 年度 | 实际值 |
|---|---|
| 1993 | 15.4 |
| 1994 | |
| 1995 | 16.5 |
| 1996 | 18 |
| 1997 | 17.5 |
| 1998 | 17.5 |
| 1999 | 17.7 |
| 2000 | 17.7 |
| 2001 | 1.21333333333333 |
| 2002 | |
| 2003 | 17.02 |
| 2004 | 26.02 |
| 2005 | 33 |
| 2006 | 30.16 |
| 2007 | 34.67 |
| 2008 | 37.96 |
| 2009 | |
| 2010 | 39.2 |
| 2011 | 40.38 |
| 2012 | 40.79 |
| 2013 | 41.02 |
| 2014 | 40.44 |
| 2015 | 42.39 |
| 2016 | 41.57 |
| 2017 | 41.75 |
| 2018 | 37.89 |