| 年度 | 实际值 |
|---|---|
| 1995 | 38.1 |
| 1996 | 35.9 |
| 1997 | 33.15 |
| 1998 | 31.9 |
| 1999 | 30.8 |
| 2000 | 30.3 |
| 2001 | 28.77 |
| 2002 | 28.8 |
| 2003 | 29.54 |
| 2004 | 31.41 |
| 2005 | 31.96 |
| 2006 | 34.17 |
| 2007 | 34.82 |
| 2008 | 34.65 |
| 2009 | |
| 2010 | 36.21 |
| 2011 | 37.51 |
| 2012 | 38.38 |
| 2013 | 39.62 |
| 2014 | 39.75 |
| 2015 | 39.46 |
| 2016 | 38.52 |
| 2017 | |
| 2018 | 30.44 |