1950,12.2
1951,12.3
1952,11.3
1953,11
1954,9.6
1955,10.8
1956,11.2
1957,10.5
1958,9.4
1959,9.3
1960,9.7
1961,9.4
1962,9.7
1963,10.4
1964,10.9
1965,11.5
1966,11.94
1967,11.7
1968,12.2
1969,12.2
1970,12.2
1971,11.4
1972,11.9
1973,12.9
1974,12.6
1975,12.6
1976,13.6
1977,13.9
1978,13.6
1979,14.9
1980,15.4
1981,15.6
1982,15.3
1983,15.9
1984,16.9
1985,17.1
1986,17.3
1987,17.8
1988,19
1989,19
1990,19.1
1991,19.1
1992,19.1
1993,19.7
1994,19.8
1995,20
1996,21
1997,21.6
1998,21.6
1999,21.5
2000,22.65
2001,21.9
2002,21.7
2003,22.4
2004,22.6
2005,22.6
2006,22.2
2007,22.9
2008,22.4
2009,20.9
2010,20.6
2011,19.8
2012,17.3
2013,17.9
2014,17.8
2015,15.8
2016,14.3
2017,13.8
2018,13.4