| 年度 | 实际值 |
|---|---|
| 1995 | 36.9 |
| 1996 | 36.6 |
| 1997 | 36.78 |
| 1998 | 36.2 |
| 1999 | 35.2 |
| 2000 | 31.3 |
| 2001 | 31.38 |
| 2002 | 30.68 |
| 2003 | 28.54 |
| 2004 | 27.66 |
| 2005 | 22.12 |
| 2006 | 22.14 |
| 2007 | 21.77 |
| 2008 | 20.28 |
| 2009 | |
| 2010 | 21.71 |
| 2011 | 22.3 |
| 2012 | 24.05 |
| 2013 | 24.35 |
| 2014 | 26.75 |
| 2015 | 28.36 |
| 2016 | 29.01 |
| 2017 | 31.5 |
| 2018 | 33.23 |