| 年度 | 实际值 |
|---|---|
| 1992 | 26.8 |
| 1993 | |
| 1994 | |
| 1995 | 28 |
| 1996 | |
| 1997 | |
| 1998 | |
| 1999 | 29.7538 |
| 2000 | 29.78 |
| 2001 | 29.9704 |
| 2002 | 30.3154 |
| 2003 | 30.3392 |
| 2004 | 30.4514 |
| 2005 | 30.2424 |
| 2006 | 30.4849 |
| 2007 | 31 |
| 2008 | 31.1758 |
| 2009 | 31.4704 |
| 2010 | 31.1033 |
| 2011 | 31 |
| 2012 | 30.5731 |
| 2013 | 30.7149 |
| 2014 | 30.4487 |
| 2015 | 30.3584 |
| 2016 | 31 |
| 2017 | 31 |