| 年度 | 实际值 |
|---|---|
| 1995 | 28.1 |
| 1996 | 29.9 |
| 1997 | 19.26 |
| 1998 | 30.1 |
| 1999 | 31.3 |
| 2000 | 29.5 |
| 2001 | 33.15 |
| 2002 | 38.08 |
| 2003 | 34.88 |
| 2004 | 28.03 |
| 2005 | 28.65 |
| 2006 | 27.69 |
| 2007 | 25.16 |
| 2008 | 22.65 |
| 2009 | |
| 2010 | 29.56 |
| 2011 | 31.04 |
| 2012 | 31.14 |
| 2013 | 31.3 |
| 2014 | 30.6 |
| 2015 | 31.5927814015501 |
| 2016 | 33.1 |
| 2017 | 35.71 |
| 2018 | 35.42 |