| 年度 | 实际值 |
|---|---|
| 1992 | 28.3 |
| 1993 | |
| 1994 | |
| 1995 | 29.6 |
| 1996 | |
| 1997 | |
| 1998 | |
| 1999 | 31.0802 |
| 2000 | 29.8262 |
| 2001 | 29.9605 |
| 2002 | 29.7412 |
| 2003 | 29.869 |
| 2004 | 30.2349 |
| 2005 | 30.4853 |
| 2006 | 31.1948 |
| 2007 | 31.9595 |
| 2008 | 32.3017 |
| 2009 | 29.03 |
| 2010 | 32.554 |
| 2011 | 32.6336 |
| 2012 | 32.6646 |
| 2013 | 30.9764 |
| 2014 | 30.5467 |
| 2015 | 29.6447 |
| 2016 | 30 |
| 2017 | 29 |