Year	% of total
1971	20.148123683475756
1972	20.520918000042155
1973	20.105677049315247
1974	19.199022998635897
1975	16.57148176768512
1976	15.90407376671874
1977	15.361658242295118
1978	14.668772014950896
1979	13.342396429180992
1980	12.29020848445925
1981	11.620902124037972
1982	11.134598961812529
1983	10.511867006872725
1984	8.409769410999496
1985	7.558393182371578
1986	7.980287416323276
1987	8.078936514084345
1988	8.207967032723614
1989	7.81204706977372
1990	11.371387318861881
1991	12.125081225592695
1992	13.921946896374823
1993	14.171181210962954
1994	15.177852650401494
1995	16.447025689925624
1996	16.736825219808956
1997	16.809247287115678
1998	16.711551820251362
1999	16.85974993366269
2000	16.17453245455956
2001	15.9590088369342
2002	16.180502097757074
2003	16.051391048892075
2004	16.02668019128078
2005	15.524014195486172
2006	15.045548121284568
2007	12.845691744400526
2008	10.539508838407553
2009	10.460513980386752
2010	9.456239574007526
2011	9.254678265019692
2012	8.56719136973063
2013	8.128650618820787
2014	7.696037533576648
2015	7.125157536788058