Year	% of total
1971	86.41509433962264
1972	86.89841833713947
1973	87.36482640865111
1974	78.97718454136272
1975	83.62629964844042
1976	83.04746159674863
1977	83.52387796433004
1978	85.23846552617937
1979	76.06720892952562
1980	66.04397255471528
1981	63.97361075869069
1982	61.69113924050633
1983	58.49625623960066
1984	55.91316990023563
1985	47.60082023239918
1986	43.56694340258755
1987	41.851915924228
1988	41.18353192246132
1989	39.66239316239316
1990	45.42102992508922
1991	46.01624005605704
1992	44.09865702479338
1993	37.801530527366495
1994	33.419750176761724
1995	38.258665052217346
1996	39.20012571697965
1997	39.56811559493873
1998	39.09140369967356
1999	37.29941291585127
2000	31.35593220338983
2001	30.280010045203415
2002	27.35936917918788
2003	30.68159814109598
2004	30.443204202232437
2005	28.403291656034703
2006	26.75434386099645
2007	27.06869353219561
2008	25.858831710709318
2009	26.513368571318335
2010	25.072822604136324
2011	27.481617647058826
2012	25.646003953685398
2013	22.262748123728695
2014	19.437895977604246
2015	19.975968759387204