| 年度 | 实际值 |
|---|---|
| 1992 | 21.3 |
| 1993 | |
| 1994 | |
| 1995 | 21.2 |
| 1996 | |
| 1997 | |
| 1998 | |
| 1999 | 20.8105 |
| 2000 | 20.7968 |
| 2001 | 20.6584 |
| 2002 | 20.4001 |
| 2003 | 20.278 |
| 2004 | 20.2244 |
| 2005 | 20.2987 |
| 2006 | 20.4433 |
| 2007 | 20.8758 |
| 2008 | 20.9508 |
| 2009 | 21.0482 |
| 2010 | 21.0849 |
| 2011 | 21.2107 |
| 2012 | 21.1401 |
| 2013 | 21.2064 |
| 2014 | 21.1843 |
| 2015 | 21.0526 |
| 2016 | 21 |
| 2017 | 21 |