Annual % of total
1960 83.1924410253646
1961 83.65489981455934
1962 84.33321618984198
1963 85.34441854082124
1964 85.4201311056283
1965 86.21466224669635
1966 85.66560058786234
1967 85.79769942971703
1968 85.75814269594846
1969 85.260793354493
1970 84.66224172654242
1971 84.15415429868938
1972 84.02431777779947
1973 82.79334872359591
1974 82.20550434887467
1975 84.05443830445232
1976 83.30431309855587
1977 82.51579585190271
1978 81.22728546457533
1979 81.42941614957023
1980 80.56398301279715
1981 79.5138438623392
1982 79.06654510745994
1983 77.0090614433204
1984 76.8489240654414
1985 75.40659270372093
1986 73.56401828516171
1987 73.79490756364362
1988 74.02295138736808
1989 75.05195139374929
1990 73.60549156089368
1991 72.29038202158334
1992 73.4363630240629
1993 72.57768591582352
1994 71.69826660191809
1995 72.52018143855318
1996 73.23708495477278
1997 74.73610579933592
1998 75.88275617826282
1999 75.63775472582364
2000 76.10257181165409
2001 76.15495344009172
2002 75.16336686415079
2003 76.54703876546589
2004 75.19713564763006
2005 75.74513788756299
2006 74.56307191429713
2007 74.73558378888558
2008 75.07600268385188
2009 75.06600051299618
2010 75.38539269213045
2011 74.69174697991518
2012 74.43947914516627
2013 73.17351572373609
2014 73.19287431821834
2015 74.089062024806