| 年度 | 实际值 |
|---|---|
| 1995 | 30.6 |
| 1996 | 29.9 |
| 1997 | 29.54 |
| 1998 | 28 |
| 1999 | 25.4 |
| 2000 | 23.4 |
| 2001 | 22.75 |
| 2002 | 22.67 |
| 2003 | 21.24 |
| 2004 | 21.01 |
| 2005 | 20.85 |
| 2006 | 18.72 |
| 2007 | 17.83 |
| 2008 | 17.52 |
| 2009 | |
| 2010 | 15.26 |
| 2011 | 13.68 |
| 2012 | 14.28 |
| 2013 | 13.73 |
| 2014 | 12.83 |
| 2015 | 11.89 |
| 2016 | 11.66 |
| 2017 | |
| 2018 | 9.62 |