| 年度 | 实际值 |
|---|---|
| 1993 | 22 |
| 1994 | |
| 1995 | 23.2 |
| 1996 | 23.9 |
| 1997 | 22.7 |
| 1998 | 23 |
| 1999 | 23.3 |
| 2000 | 23.6 |
| 2001 | 1.36666666666667 |
| 2002 | |
| 2003 | 23.31 |
| 2004 | 21.79 |
| 2005 | 22 |
| 2006 | 20.96 |
| 2007 | 25.45 |
| 2008 | 26.76 |
| 2009 | |
| 2010 | 30.56 |
| 2011 | 38.54 |
| 2012 | 39.11 |
| 2013 | 39.52 |
| 2014 | 40.28 |
| 2015 | 40.3 |
| 2016 | 37.43 |
| 2017 | 37.23 |
| 2018 | 37.27 |