| 年度 | 实际值 |
|---|---|
| 1995 | 19.3 |
| 1996 | 17.5 |
| 1997 | 30.48 |
| 1998 | 26.7 |
| 1999 | 25.1 |
| 2000 | 24.7 |
| 2001 | 23.49 |
| 2002 | 22.68 |
| 2003 | 21.98 |
| 2004 | 21.26 |
| 2005 | 19.86 |
| 2006 | 18.21 |
| 2007 | 18.25 |
| 2008 | 19.24 |
| 2009 | |
| 2010 | 18.26 |
| 2011 | 18.66 |
| 2012 | 18.73 |
| 2013 | 18.26 |
| 2014 | 18.81 |
| 2015 | 19.22 |
| 2016 | 18.9 |
| 2017 | |
| 2018 | 17.89 |