Annual % of total
1960 67.472306143001
1961 68.3495145631068
1962 62.26190476190475
1963 68.5185185185185
1964 66.58374792703151
1965 72.11703958691909
1966 69.88598256203889
1967 69.80365605958023
1968 71.92182410423452
1969 70.48458149779735
1970 72.54901960784314
1971 74.34063477872151
1972 69.33940774487472
1973 73.98250285279573
1974 76.39117550214027
1975 73.6963696369637
1976 71.95935217529374
1977 73.44110854503465
1978 74.08861469433539
1979 77.71139705882352
1980 77.39190432382705
1981 76.1332099907493
1982 76.3542562338779
1983 74.28394807335668
1984 77.00699876492382
1985 75.02052545155993
1986 67.89667896678966
1987 67.37149106817353
1988 68.36363636363637
1989 69.472
1990 76.63068108605616
1991 70.52524520255862
1992 72.01895091053049
1993 75.7536143187067
1994 72.93588695343051
1995 69.08276369863015
1996 66.30809276566286
1997 65.66263435542366
1998 61.648115942028994
1999 62.83393251533743
2000 59.29546710723941
2001 53.78332881906825
2002 52.1735432453619
2003 52.48579691180319
2004 56.974588570073514
2005 56.921335131490224
2006 56.19187269971856
2007 57.72086947412528
2008 61.07038461538461
2009 61.04894736842105
2010 64.17591688408498
2011 63.33966776258868
2012 61.988455527847044
2013 61.96198425987943
2014 56.39001798561152
2015 54.009132224861446
2016 54.98174698795181