| 年度 | 实际值 |
|---|---|
| 1978 | 2.52 |
| 1979 | 2.68 |
| 1980 | 2.85 |
| 1981 | 2.82 |
| 1982 | 2.58 |
| 1983 | 2.59 |
| 1984 | 2.86 |
| 1985 | 3.23 |
| 1986 | 3.5 |
| 1987 | 3.26 |
| 1988 | 3.5 |
| 1989 | 3.34 |
| 1990 | 4.04 |
| 1991 | 3.04 |
| 1992 | 3 |
| 1993 | 2.79 |
| 1994 | 2.75 |
| 1995 | 2.83 |
| 1996 | 2.74 |
| 1997 | 2.89 |
| 1998 | 2.81 |
| 1999 | 3 |
| 2000 | 3.08 |
| 2001 | 3.1 |
| 2002 | 2.71 |
| 2003 | 2.72 |
| 2004 | 2.89 |
| 2005 | 4.17 |
| 2006 | 9.36 |
| 2007 | 10.36 |
| 2008 | 9.93 |
| 2009 | 9.77 |
| 2010 | 10.08 |
| 2011 | 10.43 |
| 2012 | 10.1 |
| 2013 | 9.99 |
| 2014 | 9.52 |
| 2015 | 9.15 |