Year	% of total
1971	23.861535876323305
1972	25.699745547073793
1973	24.474474474474476
1974	24.271577789994502
1975	22.899131596526388
1976	20.50277918140475
1977	24.255072463768116
1978	23.893199452304884
1979	23.17573402417962
1980	27.37513707506729
1981	22.200520833333336
1982	22.249647390691113
1983	22.037071709417713
1984	22.689790019552834
1985	18.91668730905788
1986	18.744207599629288
1987	19.220334142510353
1988	19.768299881936247
1989	20.61630363517156
1990	21.49478563151796
1991	18.188095566910647
1992	23.784484072549915
1993	18.395461912479742
1994	18.536493129963443
1995	18.576560951437067
1996	20.53033811949977
1997	23.758845489496853
1998	21.044414535666217
1999	18.46638655462185
2000	12.312945666365371
2001	8.778515737799596
2002	8.538416048764955
2003	9.199965102076426
2004	13.716759431045144
2005	6.7375191183968
2006	6.078660720812925
2007	2.9902108182152283
2008	5.985198889916743
2009	5.356980169455495
2010	5.842853162440791
2011	5.991382607143768
2012	2.356826540568941
2013	1.7491840205948603
2014	1.2246861741678696
2015	1.4030797289175354