| 年度 | 实际值 |
|---|---|
| 1992 | 15 |
| 1993 | 14 |
| 1994 | 14 |
| 1995 | 14 |
| 1996 | |
| 1997 | |
| 1998 | |
| 1999 | 14.4844 |
| 2000 | 14.2898 |
| 2001 | 15.4732 |
| 2002 | 14.9666 |
| 2003 | 14.7726 |
| 2004 | 13.6008 |
| 2005 | 14.6719 |
| 2006 | 15.4538 |
| 2007 | 15.7581 |
| 2008 | 14.5062 |
| 2009 | 12.3709 |
| 2010 | 14.2932 |
| 2011 | 14.1177 |
| 2012 | 16.7472 |
| 2013 | 17.2261 |
| 2014 | 18.3033 |
| 2015 | 18.0154 |