Year	% 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