| 年度 | 实际值 |
|---|---|
| 1995 | 16.8 |
| 1996 | 16.5 |
| 1997 | 17.19 |
| 1998 | 17 |
| 1999 | 16.9 |
| 2000 | 16.5 |
| 2001 | 15.25 |
| 2002 | 14.37 |
| 2003 | 19.03 |
| 2004 | 17.45 |
| 2005 | 16.55 |
| 2006 | 15.44 |
| 2007 | 14.77 |
| 2008 | 15.44 |
| 2009 | |
| 2010 | 13.58 |
| 2011 | 13.82 |
| 2012 | 12.9 |
| 2013 | 12.48 |
| 2014 | 11.74 |
| 2015 | 10.86 |
| 2016 | 10.69 |
| 2017 | |
| 2018 | 10.46 |