Year	% of total
1971	49.583690093273
1972	45.651633793667635
1973	49.32492334308044
1974	45.63131856719902
1975	45.794528707652525
1976	44.5398147816547
1977	46.417371254214416
1978	47.29126032337285
1979	48.23777500178776
1980	48.77875077533139
1981	50.873136478328284
1982	50.74199627217808
1983	58.53619310896292
1984	58.34543941568365
1985	60.503888050543644
1986	59.70779549153193
1987	52.3327100246936
1988	51.630065539676174
1989	48.937781454837605
1990	45.55494620782996
1991	45.142532885043785
1992	44.18937729301874
1993	41.60510300769521
1994	40.044172381127844
1995	39.36665028068646
1996	38.993139339715924
1997	38.69556194197935
1998	36.76826637632789
1999	34.406639638771516
2000	35.73894966761547
2001	31.97650801050879
2002	32.03038747456003
2003	28.10742460413299
2004	28.469149450739618
2005	23.50926450061409
2006	23.531934742095274
2007	23.564165217041833
2008	24.363695997370584
2009	23.41832732830149
2010	23.50632045255307
2011	26.076801899020367
2012	26.792407750397285
2013	28.911304354885136
2014	25.080637997255817
2015	20.505629658698876