Annual % of total
1960 45.245968380851934
1961 45.128087456119154
1962 47.5248495470905
1963 51.67959004306206
1964 55.29927132161803
1965 58.28498371078945
1966 61.16301710544222
1967 62.36850427910156
1968 66.20960622280901
1969 70.24870150048375
1970 71.73903975679735
1971 71.34598882768893
1972 73.03495759413686
1973 75.01504567237586
1974 74.44119380059996
1975 76.64064439013622
1976 79.09890292173041
1977 76.47794321826169
1978 75.96878187691358
1979 72.2469173826586
1980 72.34254838606995
1981 60.44171863476109
1982 58.19475398926798
1983 54.6457122723629
1984 53.15410688528207
1985 57.66365831700414
1986 58.637358138106634
1987 60.24221203883727
1988 57.80546029962477
1989 58.236626148330714
1990 55.470176892145474
1991 56.56220557988279
1992 53.92849134072987
1993 54.80545497145328
1994 56.88474415147311
1995 52.94645719737636
1996 55.65215756007965
1997 53.265429308383325
1998 51.49752183499942
1999 50.793248584556885
2000 49.786701379617675
2001 50.33441952590889
2002 51.34684723907854
2003 54.422395752171596
2004 53.33484351947181
2005 49.1854771005222
2006 51.70609552082207
2007 49.82068828589334
2008 47.71862236401032
2009 48.47891186807439
2010 48.80002881078699
2011 46.98862801508225
2012 43.033363724621616
2013 42.6267230473743
2014 42.182526791159674
2015 40.20798298995293