| 年度 | 实际值 |
|---|---|
| 1995 | 20.5 |
| 1996 | 22.2 |
| 1997 | 21.21 |
| 1998 | 20.2 |
| 1999 | 14.1 |
| 2000 | 14.4 |
| 2001 | 13.71 |
| 2002 | 12.47 |
| 2003 | 12.55 |
| 2004 | 11.98 |
| 2005 | 11.67 |
| 2006 | 11.58 |
| 2007 | 11.12 |
| 2008 | 11.85 |
| 2009 | |
| 2010 | 10.56 |
| 2011 | 11.38 |
| 2012 | 12.68 |
| 2013 | 13.24 |
| 2014 | 12.59 |
| 2015 | 12.11 |
| 2016 | 12.13 |
| 2017 | |
| 2018 | 9.05 |