Year	% of total
1971	12.345959926623
1972	11.8895543295927
1973	12.9009577300314
1974	13.6947803138744
1975	15.3692868113622
1976	14.6476684697071
1977	15.5923448661649
1978	15.2631395191909
1979	15.4590730504047
1980	15.9901156001251
1981	16.0988573920294
1982	15.4100421910171
1983	15.238728331053
1984	14.0737502209667
1985	14.5325941656978
1986	13.031590370325
1987	13.0197911281442
1988	12.4574750999852
1989	13.1332336440229
1990	11.0145316180124
1991	11.304766992733
1992	10.6744557490647
1993	9.2404007652362
1994	9.44990450487142
1995	8.52259959520342
1996	7.75507251975072
1997	7.78107644821611
1998	5.46560478647726
1999	6.31434100042938
2000	6.99871079123008
2001	6.71889122664419
2002	6.17681986402787
2003	6.08550980967077
2004	5.83430191629851
2005	5.71239620203107
2006	5.62056887887467
2007	4.43443457039833
2008	4.84625844688116
2009	4.52691528098259
2010	4.14226115197607
2011	3.13245956492105
2012	3.13585651369086
2013	2.54861769227601
2014	2.93136532257296
2015	2.23194297048935