Annual % of total
1960 95.52018062066236
1961 95.861883084396
1962 96.43236550830402
1963 95.89151318133023
1964 96.69442997779076
1965 95.82039494328876
1966 95.15636319638
1967 95.70259703589397
1968 95.50743415058875
1969 95.53945897880669
1970 89.7415279220509
1971 89.92143247490793
1972 89.79686784546313
1973 90.26813077049546
1974 89.93530509343462
1975 88.2559046833689
1976 90.16324604147741
1977 88.0351920371777
1978 87.26473416849585
1979 86.36570693714782
1980 83.8755071961136
1981 77.75584647501749
1982 76.61918614421526
1983 72.29762216248666
1984 67.52500997564981
1985 64.3392191218306
1986 61.28573803565711
1987 60.418524016003005
1988 59.39941238744083
1989 58.848211733623465
1990 58.15395849174819
1991 57.944784449867356
1992 56.159705781616424
1993 54.19402550859748
1994 53.313483029919084
1995 53.57382198022184
1996 53.84750116460191
1997 52.90067538117532
1998 54.79426486535874
1999 54.01870151378214
2000 52.80593885211409
2001 53.400578129570896
2002 52.81353407472164
2003 52.693992518836986
2004 52.415038540393454
2005 52.29710793985124
2006 51.8924519811957
2007 51.685506010110984
2008 50.84346549626092
2009 50.851682588665255
2010 49.83637832155579
2011 48.67698651006357
2012 49.01202707006454
2013 48.54358131131076
2014 46.22592306123835
2015 46.48797087223635