Annual % of total
1960 2.230663541582478
1961 1.8942797244684038
1962 1.8929503916449086
1963 2.397706541568934
1964 2.756067461949815
1965 3.8229135507029617
1966 5.185625185625186
1967 7.031103908246589
1968 8.718594471427716
1969 10.210316061567385
1970 8.957569408067052
1971 10.104271423278464
1972 11.027780711946763
1973 12.385827561979323
1974 12.925574030087091
1975 14.645653971496667
1976 16.906507791017415
1977 17.060379021595416
1978 17.58908894340721
1979 19.277057197533487
1980 20.627348334529486
1981 21.176072139198173
1982 22.005065428450823
1983 20.87378640776699
1984 21.092993219244427
1985 21.131979046888972
1986 23.10697511083798
1987 22.69608268913402
1988 24.232769526308388
1989 25.378313253012045
1990 30.27912933847523
1991 31.358388845855927
1992 30.682674137931038
1993 32.80074340527578
1994 33.471370716510904
1995 36.586992860874105
1996 40.10742045843311
1997 39.018578698017194
1998 39.04220052310375
1999 39.17123467449491
2000 40.48265971078162
2001 43.57412078152753
2002 44.50761100125831
2003 46.752203331616
2004 47.56890406100373
2005 49.50056826304503
2006 47.315275874504145
2007 45.52090976606016
2008 45.611035263058646
2009 43.81390468227425
2010 46.9556746031746
2011 45.66747814964827
2012 44.17624683398572
2013 43.29147203140333
2014 39.35955451636722
2015 39.54408944213923
2016 41.33619154676259