| 年度 | 实际值 |
|---|---|
| 1993 | 19.4 |
| 1994 | |
| 1995 | 19.1 |
| 1996 | 19.4 |
| 1997 | 19.4 |
| 1998 | 18.6 |
| 1999 | 19 |
| 2000 | 20.4 |
| 2001 | 1.28666666666667 |
| 2002 | |
| 2003 | 19.63 |
| 2004 | 20.25 |
| 2005 | 24 |
| 2006 | 34.28 |
| 2007 | 34.28 |
| 2008 | 34.28 |
| 2009 | |
| 2010 | 37.83 |
| 2011 | 42.63 |
| 2012 | 42.73 |
| 2013 | 44.16 |
| 2014 | 44.16 |
| 2015 | 43.61 |
| 2016 | 47.38 |
| 2017 | 38.95 |
| 2018 | 39.47 |