| 年度 | 实际值 |
|---|---|
| 1995 | 21.8 |
| 1996 | 22 |
| 1997 | 20.79 |
| 1998 | 15.8 |
| 1999 | 12.9 |
| 2000 | 13.5 |
| 2001 | 13.72 |
| 2002 | 10.46 |
| 2003 | 12.74 |
| 2004 | 13.17 |
| 2005 | 15.73 |
| 2006 | 15.85 |
| 2007 | 16.07 |
| 2008 | 17.16 |
| 2009 | |
| 2010 | 16.02 |
| 2011 | 16.23 |
| 2012 | 19.21 |
| 2013 | 16.19 |
| 2014 | 16.12 |
| 2015 | 17.08 |
| 2016 | 16.76 |
| 2017 | |
| 2018 | 12.61 |