Year	% of total
1971	2.616238026743923
1972	2.9574204522090977
1973	3.3951907425087953
1974	4.00147506710632
1975	4.0851451436055415
1976	3.9463952456007068
1977	4.5671063936751
1978	4.244400274203703
1979	5.329406927859191
1980	6.408310105094111
1981	6.728211003608011
1982	7.741066943633269
1983	7.293312606024665
1984	7.533961165656821
1985	7.535026414421324
1986	7.417340428487254
1987	8.849015952600213
1988	8.711478046463345
1989	9.352810884168697
1990	20.590056146377993
1991	20.255706297602057
1992	20.755350058404474
1993	21.496507255484662
1994	23.093255233829804
1995	23.612687701994627
1996	24.108705473655604
1997	24.815600639573788
1998	25.838356433101172
1999	26.924768959843675
2000	26.23906452272641
2001	26.917471288521615
2002	28.34359606007798
2003	30.18843138920363
2004	30.931685954686998
2005	30.34792412978526
2006	28.807686738658138
2007	29.446043867094467
2008	29.624132551000965
2009	30.64967735331143
2010	30.67699963400245
2011	28.881847216005486
2012	27.410176713474733
2013	25.31120584566783
2014	25.95454937336102
2015	26.67165762569227