| 年度 | 实际值 |
|---|---|
| 1995 | 27.9 |
| 1996 | 27 |
| 1997 | 30.96 |
| 1998 | 31.7 |
| 1999 | 31.4 |
| 2000 | 31.6 |
| 2001 | 31.58 |
| 2002 | 31.79 |
| 2003 | 31.03 |
| 2004 | 30.03 |
| 2005 | 30.04 |
| 2006 | 29.26 |
| 2007 | 27.35 |
| 2008 | 25.51 |
| 2009 | |
| 2010 | 25.01 |
| 2011 | 23.11 |
| 2012 | 23.08 |
| 2013 | 24.56 |
| 2014 | 26.19 |
| 2015 | 27.5 |
| 2016 | 31.09 |
| 2017 | |
| 2018 | 38.05 |