| Year | |
|---|---|
| 1983 | 57.7 |
| 1984 | 61.0 |
| 1985 | 63.6 |
| 1986 | 66.7 |
| 1987 | 69.7 |
| 1988 | 72.3 |
| 1989 | 74.3 |
| 1990 | 77.5 |
| 1991 | 81.4 |
| 1992 | 85.4 |
| 1993 | 86.2 |
| 1994 | 87.8 |
| 1995 | 89.5 |
| 1996 | 92.0 |
| 1997 | 93.1 |
| 1998 | 93.0 |
| 1999 | 93.1 |
| 2000 | 94.3 |
| 2001 | 96.1 |
| 2002 | 97.6 |
| 2003 | 101.1 |
| 2004 | 102.5 |
| 2005 | 104.3 |
| 2006 | 106.8 |
| 2007 | 108.2 |
| 2008 | 111.5 |
| 2009 | 115.7 |
| 2010 | 116.5 |
| 2011 | 118.6 |
| 2012 | 122.6 |
| 2013 | 127.6 |
| 2014 | 126.7 |
| 2015 | 128.7 |
| 2016 | 131.0 |
| 2017 | 132.6 |
| 2018 | 134.1 |
| 2019 | 137.1 |