| 年度 | 实际值 |
|---|---|
| 1995 | 33.5 |
| 1996 | 33.1 |
| 1997 | 62.3 |
| 1998 | 40.3 |
| 1999 | 34.9 |
| 2000 | 33.9 |
| 2001 | 32.14 |
| 2002 | 30.29 |
| 2003 | 31.13 |
| 2004 | 32.48 |
| 2005 | 21.89 |
| 2006 | 20.18 |
| 2007 | 19.64 |
| 2008 | 18.81 |
| 2009 | |
| 2010 | 17.61 |
| 2011 | 19.23 |
| 2012 | 18.66 |
| 2013 | 18.45 |
| 2014 | 16.54 |
| 2015 | 17.54 |
| 2016 | 17.42 |
| 2017 | 15.31 |
| 2018 | 14.18 |