| 年度 | 实际值 |
|---|---|
| 1995 | 16.5 |
| 1996 | 17.6 |
| 1997 | 17.55 |
| 1998 | 35 |
| 1999 | 34.6 |
| 2000 | 32.9 |
| 2001 | 31.59 |
| 2002 | 29.83 |
| 2003 | 27.21 |
| 2004 | 25.96 |
| 2005 | 24.29 |
| 2006 | 21.99 |
| 2007 | 21.2 |
| 2008 | 19.42 |
| 2009 | |
| 2010 | 18.42 |
| 2011 | 18.31 |
| 2012 | 18.31 |
| 2013 | 18.06 |
| 2014 | 17.68 |
| 2015 | 17.47 |
| 2016 | 17.58 |
| 2017 | |
| 2018 | 19.64 |