| 年度 | 实际值 |
|---|---|
| 1995 | 16 |
| 1996 | 18.3 |
| 1997 | 18.76 |
| 1998 | 19.8 |
| 1999 | 19.4 |
| 2000 | 19.1 |
| 2001 | 19.01 |
| 2002 | 18.64 |
| 2003 | 17.43 |
| 2004 | 16.45 |
| 2005 | 16.19 |
| 2006 | 15.09 |
| 2007 | 14.3 |
| 2008 | 13.71 |
| 2009 | |
| 2010 | 13.73 |
| 2011 | 13.47 |
| 2012 | 13.79 |
| 2013 | 13.35 |
| 2014 | 14.15 |
| 2015 | 15.91 |
| 2016 | 17.01 |
| 2017 | |
| 2018 | 16.69 |