Annual % of total
1960 84.4501201923077
1961 82.36727090348928
1962 84.01966810079901
1963 81.2197979206326
1964 81.19365664275844
1965 80.45848128075748
1966 76.98919735160878
1967 75.99865726753944
1968 76.14523063856893
1969 78.39529590288315
1970 77.32913748781135
1971 78.00362826750225
1972 76.92589278451152
1973 75.76407297676595
1974 74.8254163149413
1975 72.6514215080346
1976 72.07849478171396
1977 72.19311649567052
1978 71.08252947481243
1979 71.48630295803108
1980 70.41783293427308
1981 68.71383907715528
1982 66.79903559778755
1983 65.3248292206887
1984 63.16912802506109
1985 60.12831261619218
1986 59.73468454203174
1987 57.86249800606157
1988 54.56740928575741
1989 51.072625348407506
1990 59.331648637820514
1991 58.18733763767566
1992 59.324442477876104
1993 60.52878411240204
1994 59.09859766277129
1995 55.25470784641069
1996 52.13073957016435
1997 52.562637448947534
1998 52.28855072463768
1999 53.7083374319994
2000 50.69750511712531
2001 51.02436533995355
2002 48.98490167702392
2003 46.280305391087566
2004 47.845495946422275
2005 49.1105330781848
2006 52.76401621934737
2007 47.677947197946594
2008 52.76859887005651
2009 52.368412093495934
2010 53.65719103128346
2011 49.06779476475234
2012 47.97930487873186
2013 49.3669875
2014 48.683394475015284
2015 49.23620936106185
2016 48.183599956587805