| 年度 | 实际值 |
|---|---|
| 1992 | 20.8 |
| 1993 | 21.8 |
| 1994 | 22.82 |
| 1995 | 23.53 |
| 1996 | 24.16 |
| 1997 | 24.78 |
| 1998 | 25.42 |
| 1999 | 26.2 |
| 2000 | 26.75 |
| 2001 | 27.22 |
| 2002 | 27.85 |
| 2003 | 27.99 |
| 2004 | 28.32 |
| 2005 | 28.5 |
| 2006 | 28.69 |
| 2007 | 28.78 |
| 2008 | 28.99 |
| 2009 | |
| 2010 | 29.2 |
| 2011 | 29.8 |
| 2012 | 29.9 |
| 2013 | 29.9 |
| 2014 | 30.1 |
| 2015 | 29.31 |
| 2016 | 64 |
| 2017 | 63 |
| 2018 | 63 |