| 年度 | 实际值 |
|---|---|
| 1995 | 30.2 |
| 1996 | 29.3 |
| 1997 | 26.04 |
| 1998 | 24.2 |
| 1999 | 22.1 |
| 2000 | 32.2 |
| 2001 | 29.8 |
| 2002 | 24.8 |
| 2003 | 25.82 |
| 2004 | 24.12 |
| 2005 | 22.64 |
| 2006 | 20.26 |
| 2007 | 20.02 |
| 2008 | 21.82 |
| 2009 | |
| 2010 | 17.31 |
| 2011 | 15.52 |
| 2012 | 15.08 |
| 2013 | 14.21 |
| 2014 | 15.11 |
| 2015 | 18.08 |
| 2016 | 17.69 |
| 2017 | |
| 2018 | 17.56 |