Year	% of total
1960	48.316707668667455
1961	49.222438624733286
1962	50.18707924370286
1963	47.07290008182575
1964	48.18426002714909
1965	44.722665022097246
1966	41.66473887365123
1967	43.218661185398204
1968	42.32735471601287
1969	40.56913987715639
1970	40.09821101170112
1971	40.32671050623593
1972	37.23959848298228
1973	34.852981271668106
1974	34.149134261921986
1975	32.90013398129991
1976	36.05096649775481
1977	34.74579510719398
1978	34.98153511478901
1979	34.97078065653256
1980	35.898010249326134
1981	35.96590315315824
1982	37.832930587516095
1983	37.939540723022716
1984	36.72184672396753
1985	35.18700290050138
1986	33.922221754229554
1987	32.96346439055654
1988	32.120291029563305
1989	32.872506934042086
1990	32.71129450271824
1991	31.653776580552318
1992	30.608118433994143
1993	29.40206875939606
1994	29.24839917151751
1995	29.240333278405995
1996	28.17388402117327
1997	27.437266241576463
1998	27.678855733781244
1999	26.801916828756784
2000	27.310948436837705
2001	26.221805695050172
2002	26.98888384744562
2003	26.79215280793298
2004	26.063946618837075
2005	25.1092616590119
2006	24.19949035001775
2007	24.660250072179295
2008	21.861973135710976
2009	20.985357675786766
2010	20.074911017299893
2011	21.100698196326157
2012	22.66295393475086
2013	22.376878598635454
2014	21.79711449423283
2015	22.05536148655632