| 年度 | 实际值 |
|---|---|
| 1992 | 22.4 |
| 1993 | |
| 1994 | |
| 1995 | 23 |
| 1996 | |
| 1997 | |
| 1998 | |
| 1999 | 23.6 |
| 2000 | 22.76 |
| 2001 | 22.6 |
| 2002 | 22.82 |
| 2003 | 22.99 |
| 2004 | 23.2 |
| 2005 | 22.56 |
| 2006 | 22.61 |
| 2007 | 22.55 |
| 2008 | 22.57 |
| 2009 | 22.47 |
| 2010 | 22.29 |
| 2011 | 22.24 |
| 2012 | 21.85 |
| 2013 | 21.86 |
| 2014 | 21.79 |
| 2015 | 21.57 |
| 2016 | 21.6 |
| 2017 | 21.2 |
| 2018 | 21.169 |