| 年度 | 实际值 |
|---|---|
| 1995 | 19.6 |
| 1996 | 19 |
| 1997 | 18.04 |
| 1998 | 17.7 |
| 1999 | 15.9 |
| 2000 | 13.7 |
| 2001 | 13.1 |
| 2002 | 12.42 |
| 2003 | 10.05 |
| 2004 | 10.46 |
| 2005 | 10.44 |
| 2006 | 10.54 |
| 2007 | 11.42 |
| 2008 | 11.26 |
| 2009 | |
| 2010 | 13.62 |
| 2011 | 13.08 |
| 2012 | 13.38 |
| 2013 | 14.67 |
| 2014 | 14.55 |
| 2015 | 14.21 |
| 2016 | 14.52 |
| 2017 | |
| 2018 | 12.43 |