| 年度 | 实际值 |
|---|---|
| 1978 | 5.8 |
| 1979 | |
| 1980 | 6.1 |
| 1981 | |
| 1982 | |
| 1983 | |
| 1984 | |
| 1985 | 7 |
| 1986 | |
| 1987 | |
| 1988 | |
| 1989 | |
| 1990 | 7.8 |
| 1991 | |
| 1992 | |
| 1993 | |
| 1994 | |
| 1995 | 8 |
| 1996 | |
| 1997 | |
| 1998 | |
| 1999 | 8.2 |
| 2000 | 8.2 |
| 2001 | 8.1 |
| 2002 | 8.1 |
| 2003 | 8.3 |
| 2004 | 8.4 |
| 2005 | 9.2 |
| 2006 | 9.2 |
| 2007 | 9.2 |
| 2008 | 9.3 |
| 2009 | 9.3 |
| 2010 | 9.1 |
| 2011 | 9.16 |
| 2012 | 9.22 |
| 2013 | 9.25 |
| 2014 | 9.34 |