| 年度 | 实际值 |
|---|---|
| 1992 | 22.6 |
| 1993 | |
| 1994 | |
| 1995 | 23.1 |
| 1996 | |
| 1997 | |
| 1998 | |
| 1999 | 23.6 |
| 2000 | 23.9 |
| 2001 | 24 |
| 2002 | 23.9 |
| 2003 | 24 |
| 2004 | 24 |
| 2005 | 24.3 |
| 2006 | 24.7 |
| 2007 | 25.5065 |
| 2008 | 26.28 |
| 2009 | 26.9 |
| 2010 | 28.0833 |
| 2011 | 28.23 |
| 2012 | 28.2656 |
| 2013 | 27.62 |
| 2014 | 28.17 |
| 2015 | 28.68 |
| 2016 | 29.1231 |
| 2017 | 29 |