Annual % of total
1960 2.9473100805050114
1961 4.049153105280637
1962 4.9464138499587795
1963 5.333031035872632
1964 6.351657574485942
1965 7.359070562947326
1966 8.52798002328746
1967 9.817680119176599
1968 10.383334115328672
1969 11.590455740912496
1970 12.275807662696865
1971 13.710365598594496
1972 14.860870010195123
1973 16.411231088428163
1974 18.49395399244342
1975 17.838417464229696
1976 19.99509510890391
1977 19.666689988106068
1978 19.301695102285468
1979 18.64089959082747
1980 18.63601486602334
1981 17.6771223864911
1982 16.327757163973722
1983 15.835795188329161
1984 14.968985513102865
1985 14.483557219682108
1986 14.660243560499318
1987 14.562399496841149
1988 14.49295772468193
1989 14.728043665263431
1990 15.209708239776202
1991 15.477381232652387
1992 15.966943362363429
1993 16.224504885512932
1994 15.342784254133651
1995 15.190697306531556
1996 16.674077092740987
1997 17.84853192271427
1998 17.317422589507814
1999 18.964836244125493
2000 19.413851929822464
2001 18.70957623874672
2002 17.162923066015814
2003 16.488662633403575
2004 16.396086359758133
2005 14.621947614072232
2006 13.98137428850839
2007 12.942525797020982
2008 13.494235449290551
2009 12.343235948677336
2010 12.909006088138108
2011 12.122748470886211
2012 12.35339812088478
2013 12.43506201266419
2014 12.775282871851672
2015 13.515829012566083
2016 13.616829028225114