| 年度 | 实际值 |
|---|---|
| 1992 | 15.2 |
| 1993 | 15.1 |
| 1994 | |
| 1995 | 14.25 |
| 1996 | 14.31 |
| 1997 | 13.7 |
| 1998 | 4.32 |
| 1999 | 13.19 |
| 2000 | 14.08 |
| 2001 | 9.23 |
| 2002 | 9.82 |
| 2003 | 9.93 |
| 2004 | 9.42 |
| 2005 | 9.47 |
| 2006 | 8.13 |
| 2007 | 7.97 |
| 2008 | 11.38 |
| 2009 | |
| 2010 | 19.3 |
| 2011 | 18.4 |
| 2012 | 9.9 |
| 2013 | 8 |
| 2014 | 6.4 |
| 2015 | 6.01 |
| 2016 | 8.56 |
| 2017 | 10.35 |
| 2018 | 17.16 |