Annual % of total
1960 79.27944331078322
1961 77.32761287782193
1962 71.03618719563907
1963 68.90464499196698
1964 68.58344973674375
1965 67.66464047125464
1966 67.62703985108193
1967 69.12395047482313
1968 68.41395434874325
1969 69.22637580372401
1970 69.9876103527597
1971 67.66302918989065
1972 69.62796188513278
1973 70.8268326379455
1974 68.61008304981176
1975 65.00361579427612
1976 69.22466162442231
1977 71.11573670773895
1978 69.10094335196196
1979 65.77572560264993
1980 64.76561959158306
1981 64.544190830369
1982 68.04110192203603
1983 66.94057402904706
1984 68.26025083545096
1985 71.37562006193228
1986 69.68552295830463
1987 69.36143404330706
1988 69.38861502570236
1989 67.44439608916358
1990 66.7463465777713
1991 67.04698352888518
1992 69.03009345670714
1993 68.30793359404488
1994 68.45249391920586
1995 67.8919243370432
1996 69.80940309541442
1997 72.05136330383006
1998 69.59774064490503
1999 70.81706548813462
2000 69.46326290235095
2001 71.80383968091236
2002 69.7739777662775
2003 70.01993546116283
2004 68.25817539887932
2005 68.18112114942768
2006 67.62940923656356
2007 67.5792870182821
2008 66.85097419240397
2009 64.13140864228005
2010 61.05375011444546
2011 59.75881494619944
2012 62.236579812626566
2013 60.83265376506635
2014 59.84684405263516
2015 59.74916853612227