| 年度 | 实际值 |
|---|---|
| 1992 | 57.2 |
| 1993 | |
| 1994 | |
| 1995 | 57.4 |
| 1996 | |
| 1997 | |
| 1998 | |
| 1999 | 57.8 |
| 2000 | 57.7 |
| 2001 | 57.5 |
| 2002 | 57.2 |
| 2003 | 56.9 |
| 2004 | 56.6 |
| 2005 | 56.3 |
| 2006 | 56.3 |
| 2007 | 56.55 |
| 2008 | 56.9 |
| 2009 | 57.1 |
| 2010 | 57.1 |
| 2011 | 57.1 |
| 2012 | 56.8 |
| 2013 | 56.7 |
| 2014 | 56.8 |
| 2015 | 56.65 |
| 2016 | 56.5815 |
| 2017 | 56.5 |
| 2018 | 56.282 |