1950 28.5498
1951 29.52686
1952 29.86572
1953 28.94763
1954 26.62955
1955 28.98581
1956 31.87842
1957 26.15994
1958 30.57617
1959 30.72473
1960 31.77466
1961 33.13474
1962 29.0076
1963 28.38181
1964 27.87445
1965 31.98282
1966 29.2453
1967 31.32135
1968 29.73309
1969 29.56235
1970 30.93198
1971 31.92966
1972 32.5817
1973 29.54471
1974 28.96841
1975 30.3125
1976 26.75284
1977 31.98566
1978 31.59009
1979 32.10062
1980 29.89642
1981 32.42026
1982 30.22833
1983 31.31912
1984 31.46207
1985 31.50497
1986 31.06262
1987 30.50623
1988 33.11829
1989 28.67215
1990 32.32654
1991 30.19131
1992 31.22025
1993 27.91937
1994 33.01016
1995 28.78726
1996 31.25589
1997 30.00058
1998 33.15329
1999 28.62372
2000 28.96475
2001 29.89221
2002 30.73383
2003 31.87512
2004 31.50314
2005 28.90686
2006 33.98495
2007 31.75519
2008 32.46198
2009 32.16949
2010 29.69861
2011 29.17456
2012 31.22369
2013 32.31827
2014 32.15482
2015 33.54721
2016 30.12253
2017 32.47925
2018 33.08316
2019 29.7251
2020 32.71844
2021 39.65491