| 年度 | 实际值 |
|---|---|
| 1992 | 28.7 |
| 1993 | |
| 1994 | |
| 1995 | 29 |
| 1996 | |
| 1997 | |
| 1998 | |
| 1999 | 15.8423 |
| 2000 | 16.1812 |
| 2001 | 29.2595 |
| 2002 | 29.4403 |
| 2003 | 29.6229 |
| 2004 | 29.7106 |
| 2005 | 30.0809 |
| 2006 | 30.1506 |
| 2007 | 30.1306 |
| 2008 | 30.2923 |
| 2009 | 31.4823 |
| 2010 | 29.7871 |
| 2011 | 28.9576 |
| 2012 | 29.8356 |
| 2013 | 31.7875 |
| 2014 | 32.27 |
| 2015 | 31.2333 |