| 年度 | 实际值 |
|---|---|
| 1992 | 3 |
| 1993 | |
| 1994 | |
| 1995 | 2.9 |
| 1996 | |
| 1997 | |
| 1998 | |
| 1999 | 2.8399 |
| 2000 | 2.9084 |
| 2001 | 2.8451 |
| 2002 | 2.889 |
| 2003 | 2.8883 |
| 2004 | 2.8744 |
| 2005 | 2.8385 |
| 2006 | 2.7828 |
| 2007 | 2.7771 |
| 2008 | 2.6953 |
| 2009 | 2.7721 |
| 2010 | 2.7683 |
| 2011 | 2.7953 |
| 2012 | 2.8394 |
| 2013 | 2.8449 |
| 2014 | 2.6733 |
| 2015 | 2.8726 |