Year	% of total
1971	37.240614893131344
1972	36.645105287880746
1973	39.57208837305187
1974	34.455117871747646
1975	33.82128369244269
1976	32.34970199929703
1977	32.71555554855862
1978	36.69451865300689
1979	38.691512276212805
1980	43.57856657643627
1981	44.93386886680161
1982	46.1999599186388
1983	47.32226280813871
1984	46.69982130039758
1985	46.43078698629524
1986	46.26352486573587
1987	44.33565711238245
1988	43.16114941606139
1989	42.05749373737365
1990	57.24440274952053
1991	54.818333089902374
1992	53.63548437701642
1993	53.54971174134452
1994	53.717874123379175
1995	55.283557345782654
1996	54.64942333928664
1997	54.603717507715245
1998	54.263208732018576
1999	53.32179263610143
2000	53.842613270020635
2001	55.86142077442513
2002	56.4796260100238
2003	55.83723116032904
2004	54.18963494870908
2005	49.76666297852665
2006	49.54757264592351
2007	49.894135506080836
2008	51.34959645486984
2009	50.55649453930599
2010	53.198104937577554
2011	51.84593416521018
2012	52.970212690560594
2013	52.065988613357064
2014	51.19755963956278
2015	51.384336808729245