Year	% of total
1971	19.595171983251625
1972	19.689601462811464
1973	21.285183298679737
1974	22.348526001970754
1975	20.984238613507205
1976	19.652625375571223
1977	19.34897826281676
1978	18.164155365294825
1979	16.72594593287017
1980	15.995557179702882
1981	15.423412620669433
1982	15.757930873369878
1983	15.422218630068402
1984	12.020512666536389
1985	11.400337849414427
1986	11.234603638896177
1987	11.098474502072078
1988	10.98569655000888
1989	10.793711928467939
1990	10.134411505834857
1991	13.695655612364247
1992	13.360995287995012
1993	13.23579068634638
1994	12.72346130380865
1995	14.00699300255205
1996	12.993943821059458
1997	12.945376701434691
1998	13.4743951876018
1999	13.998817033325336
2000	14.30808145518188
2001	13.886649801187263
2002	14.206755610266175
2003	13.40584631696237
2004	12.96253599987192
2005	14.474156940321583
2006	13.549273585183808
2007	12.983630867509302
2008	16.190093967142296
2009	16.501331151964642
2010	15.406353565519263
2011	13.804367436961714
2012	13.575217951773347
2013	14.056266694442312
2014	12.90926874592758
2015	13.271691338655451