Annual % of total
1960 10.115036021380433
1961 12.313998540064011
1962 18.585138785127292
1963 17.583024810742113
1964 18.12796208530806
1965 20.969785575048736
1966 21.03760761214318
1967 22.009686215457243
1968 21.111154461394406
1969 19.172581917258196
1970 18.08216535939308
1971 15.911531651815517
1972 16.2864736171862
1973 16.661160385270275
1974 16.200231837429914
1975 15.64924641041648
1976 13.68714527531614
1977 13.753565316600113
1978 15.060032610306834
1979 16.986618356752476
1980 16.32608458092012
1981 16.640890813485925
1982 17.02032960423433
1983 18.654849075488595
1984 18.906602913788323
1985 18.934858595487768
1986 16.457729032579334
1987 15.994368684157154
1988 16.176646206023552
1989 24.380604955160358
1990 19.78563615988046
1991 19.333459629500176
1992 19.208215764770845
1993 18.31976298906359
1994 17.469939873611878
1995 18.585033603027533
1996 19.258272509813544
1997 18.848986914068092
1998 19.068164129502573
1999 19.380258273920163
2000 21.13713431127757
2001 21.672816908767896
2002 23.72975562072336
2003 25.058133660933663
2004 25.52796494362491
2005 24.4229205115752
2006 26.24655800404705
2007 25.382164961830412
2008 24.855809471942354
2009 26.752836105336105
2010 26.49023158613042
2011 27.198289046906186
2012 28.25751097335192
2013 30.305469075894948
2014 30.244429001570953
2015 31.337761907784756
2016 31.628401043296815