1928 0.2065 1929 0.2069 1930 0.2067 1931 0.2080 1932 0.2098 1933 0.2410 1934 0.2007 1935 0.2063 1936 0.2034 1937 0.2042 1938 0.2065 1939 0.2272 1940 0.2513 1941 0.2513 1942 0.2513 1943 0.2513 1944 0.2513 1945 0.2506 1946 0.2497 1947 0.2495 1948 0.2495 1949 0.2728 1950 0.3592 1951 0.3593 1952 0.3595 1953 0.3569 1954 0.3574 1955 0.3596 1956 0.3590 1957 0.3593 1958 0.3572 1959 0.3574 1960 0.3575 1961 0.7164 1962 0.7149 1963 0.7169 1964 0.7190 1965 0.7180 1966 0.7188 1967 0.7190 1968 0.7189 1969 0.7199 1970 0.7182 1971 0.7128 1972 0.7726 1973 0.6950 1974 0.6804 1975 0.7328 1976 0.8707 1977 0.8696 1978 0.8695 1979 0.8423 1980 0.7780 1981 0.8713 1982 1.0835 1983 1.1130 1984 1.4382 1985 2.2343 1986 2.2919 1987 2.0385 1988 2.2770 1989 2.6214 1990 2.5885 1991 2.7633 1992 2.8524 1993 3.2729 1994 3.5526 1995 3.6284 1996 4.3011 1997 4.6072 1998 5.5417 1999 6.1191 2000 6.9468 2001 8.6093 2002 10.517 2003 7.5550 2004 6.4402 2005 6.3606 2006 6.7668 2007 7.0477 2008 8.2480 2009 8.4117 2010 7.3161 2011 7.2510