Year	% of total
1971	44.0527450950137
1972	43.90969750683862
1973	44.52487506539403
1974	43.61820559277191
1975	42.4134092101401
1976	44.07806756349465
1977	41.34980587875309
1978	41.66944804954693
1979	41.16673261221282
1980	40.96081847395546
1981	38.54393593102874
1982	37.90710698704013
1983	36.54147382678052
1984	34.61280483008947
1985	33.16591961703846
1986	32.94704377733426
1987	32.36356817679762
1988	30.996556344248443
1989	32.2205555234601
1990	60.77524001710499
1991	59.96533792796568
1992	58.222535589723215
1993	55.924725175582125
1994	55.516414401363114
1995	55.23613467547087
1996	55.00292361432971
1997	54.31922486561843
1998	54.511703545972765
1999	54.33076726209355
2000	54.68778203422309
2001	54.23486981654687
2002	55.092826218088454
2003	56.33300183429395
2004	55.24784570716144
2005	55.59865668944495
2006	56.12882637347772
2007	56.88130739730849
2008	56.52301655276627
2009	54.71408675147881
2010	54.009884429039815
2011	54.18943942652984
2012	52.77203864706937
2013	50.73090609209706
2014	49.446564555553095
2015	48.97388388244428