| 年度 | 实际值 |
|---|---|
| 1995 | 22.6 |
| 1996 | 22.1 |
| 1997 | 15.87 |
| 1998 | 19.5 |
| 1999 | 13.8 |
| 2000 | 14.3 |
| 2001 | 11.51 |
| 2002 | 12.81 |
| 2003 | 14.67 |
| 2004 | 14.55 |
| 2005 | 16.2 |
| 2006 | 16.37 |
| 2007 | 15.25 |
| 2008 | 16.5 |
| 2009 | |
| 2010 | 15.83 |
| 2011 | 16.12 |
| 2012 | 16.68 |
| 2013 | 18.32 |
| 2014 | 17.76 |
| 2015 | 17.87 |
| 2016 | 18.15 |
| 2017 | |
| 2018 | 14.75 |