Year	% of total
1971	0
1972	0
1973	0
1974	0
1975	0
1976	0
1977	0
1978	0.019302535066272036
1979	3.8256281105714454
1980	11.533122327725026
1981	16.75725125114352
1982	20.01442852725961
1983	22.979397781299525
1984	25.302171860245515
1985	25.999297197575334
1986	26.566224849814056
1987	21.667697199894
1988	21.276335628998737
1989	22.32432643804012
1990	22.39905800129145
1991	22.449218293110842
1992	22.03324313877078
1993	21.321343918130857
1994	20.74103245709035
1995	18.277423583387954
1996	17.790726168758678
1997	18.184787798075234
1998	21.43922266583289
1999	25.569608032438694
2000	25.670125855597263
2001	22.193411264612113
2002	21.131904182227082
2003	18.553078957310163
2004	18.374823525206853
2005	17.538494175049056
2006	18.524910624658787
2007	17.235074063511767
2008	17.732362177537365
2009	16.77782981540996
2010	14.779604971804789
2011	14.636579160402452
2012	14.385430808683369
2013	13.092232880716391
2014	13.77132354844555
2015	14.899348403771251