| 年度 | 实际值 |
|---|---|
| 1992 | 31.3 |
| 1993 | |
| 1994 | |
| 1995 | 31.7 |
| 1996 | |
| 1997 | |
| 1998 | |
| 1999 | 18.4846 |
| 2000 | 18.76 |
| 2001 | 30.2478 |
| 2002 | 29.3877 |
| 2003 | 30.7382 |
| 2004 | 30.8164 |
| 2005 | 30.5745 |
| 2006 | 29.5806 |
| 2007 | 30.5139 |
| 2008 | 30.5219 |
| 2009 | 31.7987 |
| 2010 | 31.8063 |
| 2011 | 31.9088 |
| 2012 | 32.1795 |
| 2013 | 32.2855 |
| 2014 | 31.0628 |
| 2015 | 29.6583 |