| 年度 | 实际值 |
|---|---|
| 1992 | 30.1 |
| 1993 | |
| 1994 | |
| 1995 | 30.4 |
| 1996 | |
| 1997 | |
| 1998 | |
| 1999 | 30.7359 |
| 2000 | 30.2405 |
| 2001 | 30.1044 |
| 2002 | 30.3126 |
| 2003 | 30.5593 |
| 2004 | 30.8193 |
| 2005 | 30.7153 |
| 2006 | 31.316 |
| 2007 | 31.3584 |
| 2008 | 31.5783 |
| 2009 | 31.4601 |
| 2010 | 31.281 |
| 2011 | 31.3205 |
| 2012 | 31.368 |
| 2013 | 31.4678 |
| 2014 | 31.3185 |
| 2015 | 30.3814 |
| 2016 | 30 |
| 2017 | 31 |