Annual % of total
1960 21.812761638969935
1961 22.11194863027214
1962 22.660654858283444
1963 23.051954922397965
1964 23.33210949659766
1965 23.09830185149338
1966 23.66438698160157
1967 23.865655780891405
1968 24.459428418292145
1969 25.316270013730467
1970 24.48837487071189
1971 25.198173220817736
1972 24.45998550857356
1973 23.15173840983239
1974 22.899493548343365
1975 22.216479959920672
1976 21.574891653762627
1977 20.320900687036772
1978 20.058556701030927
1979 20.72389977946215
1980 21.215638443484668
1981 21.40115318321902
1982 20.9786446718963
1983 19.766291876717105
1984 19.819550375451904
1985 19.15795127214967
1986 18.183998355526118
1987 18.464706761118816
1988 18.547538457387326
1989 18.954045215476185
1990 20.722036495431365
1991 21.845392744312193
1992 21.945719868038193
1993 22.024440469167157
1994 22.15091407249425
1995 22.66889633111627
1996 21.813579955745766
1997 20.928045598496034
1998 20.432208900495468
1999 21.40335014170365
2000 21.728860901494183
2001 20.51561885463321
2002 21.910386617472508
2003 21.025982935280222
2004 20.360687487696058
2005 20.204659837945268
2006 20.355662485105842
2007 21.683663155217438
2008 22.30247392753274
2009 23.799981723212294
2010 23.643710528902048
2011 25.213469847837437
2012 27.57733696146224
2013 27.354400609097162
2014 28.228809739386744
2015 29.785640394236967
2016 30.653846877659223