| 年度 | 实际值 |
|---|---|
| 1992 | 23.3 |
| 1993 | |
| 1994 | |
| 1995 | 23.6 |
| 1996 | |
| 1997 | |
| 1998 | |
| 1999 | 23.8 |
| 2000 | 25.1911 |
| 2001 | 25.0761 |
| 2002 | 25.0098 |
| 2003 | 24.8813 |
| 2004 | 24.818 |
| 2005 | 25.31 |
| 2006 | 25.45 |
| 2007 | 25.38 |
| 2008 | 25.43 |
| 2009 | 25.9187 |
| 2010 | 26.3077 |
| 2011 | 26.5165 |
| 2012 | 26.684 |
| 2013 | 26.9332 |
| 2014 | 25.14 |
| 2015 | 25.2038833705541 |
| 2016 | 27 |
| 2017 | 27 |