Year	% of total
1971	44.29498562861185
1972	42.299276182224546
1973	42.80897242228618
1974	41.38636304277718
1975	42.49944504734079
1976	39.687532939171824
1977	41.97251507265178
1978	42.43791521362682
1979	43.70403424416968
1980	38.492382476426194
1981	42.621373623426024
1982	47.0830547325364
1983	48.567372256668115
1984	47.587496583320565
1985	47.67350323178893
1986	47.93482022946115
1987	47.75830422049776
1988	47.350815160839474
1989	45.51992920083486
1990	35.802350933269565
1991	36.59352886024295
1992	35.71059863694566
1993	32.26689584527055
1994	31.864752466853208
1995	31.415467298149835
1996	30.93178946675266
1997	32.333892724907834
1998	34.374406311088556
1999	34.130251997714396
2000	34.40706883023946
2001	31.889452811261833
2002	33.08126311418476
2003	32.497151413588384
2004	31.52360777320912
2005	27.408012626134465
2006	26.42676110401638
2007	26.87909331008148
2008	27.076683606367556
2009	24.259270911221577
2010	22.7698101267259
2011	22.890488844796508
2012	24.094001394542126
2013	22.732907922126227
2014	23.08517153879385
2015	20.43807520406115