| 年度 | 实际值 |
|---|---|
| 1992 | 26.1 |
| 1993 | |
| 1994 | |
| 1995 | 27.9 |
| 1996 | |
| 1997 | |
| 1998 | |
| 1999 | 30.3047 |
| 2000 | 28.2683 |
| 2001 | 28.4579 |
| 2002 | 28.5939 |
| 2003 | 28.8556 |
| 2004 | 27.6059 |
| 2005 | 27.1942 |
| 2006 | 28.0496 |
| 2007 | 28.8646 |
| 2008 | 30.0957 |
| 2009 | 27.6 |
| 2010 | 29.7882 |
| 2011 | 29.8983 |
| 2012 | 29.4797 |
| 2013 | 29.1549 |
| 2014 | 28.1408 |
| 2015 | 28.0377 |
| 2016 | 28 |
| 2017 | 28 |