Year	% of total
1971	32.3513068474311
1972	31.257423337833433
1973	30.598498146352647
1974	28.857194857397634
1975	28.00511358420997
1976	27.807922778079465
1977	28.247015303383026
1978	28.28569315620853
1979	25.982474989653927
1980	25.397022063475035
1981	24.26461969324802
1982	23.73686659881123
1983	23.78819832226428
1984	21.996604410073452
1985	20.44704693241857
1986	22.36107440685749
1987	22.462552653358443
1988	21.671104119171343
1989	21.09169733104592
1990	18.94052115896166
1991	18.77007405077891
1992	19.096437896062508
1993	17.1952148908136
1994	18.700938606478807
1995	17.13670378396662
1996	16.93414480323694
1997	17.840222074565677
1998	19.27991001662816
1999	18.613596030258915
2000	18.145858227661545
2001	18.127390376296564
2002	15.308812523020258
2003	13.502327531020827
2004	13.140095222828812
2005	12.821828272733276
2006	11.819663993450991
2007	11.370460113952486
2008	11.295504140443661
2009	10.73291478042122
2010	10.197877935425883
2011	10.36004356062346
2012	10.906618200034785
2013	10.780094160761717
2014	10.035718779568642
2015	9.75328147147959