| 年度 | 实际值 |
|---|---|
| 1995 | 31 |
| 1996 | 29.5 |
| 1997 | 29.78 |
| 1998 | 29.3 |
| 1999 | 27.9 |
| 2000 | 26.6 |
| 2001 | 26.42 |
| 2002 | 25.54 |
| 2003 | 21.39 |
| 2004 | 20.49 |
| 2005 | 22.03 |
| 2006 | 21.56 |
| 2007 | 22.49 |
| 2008 | 22.58 |
| 2009 | |
| 2010 | 20.59 |
| 2011 | 20.24 |
| 2012 | 20.69 |
| 2013 | 20.46 |
| 2014 | 19.01 |
| 2015 | 19.1 |
| 2016 | 19.25 |
| 2017 | |
| 2018 | 17.74 |