Year	% of total
1971	16.54080510338
1972	17.485317596225016
1973	18.417876411248763
1974	18.62006886029
1975	19.243854205747457
1976	21.082916322187668
1977	21.928926616455033
1978	23.252101270185797
1979	24.429558782101143
1980	24.45400942820354
1981	24.48085356197369
1982	24.87611342413453
1983	25.84592170727702
1984	25.330918812133305
1985	26.334935700706993
1986	26.32760534676866
1987	26.16770750288578
1988	27.77633319922056
1989	28.49023602448254
1990	27.917092618449555
1991	26.182983459993352
1992	29.51920727082464
1993	31.569370923178816
1994	31.11487981245695
1995	30.307427078760977
1996	30.61316757613274
1997	32.6423901050322
1998	27.655426709008925
1999	25.97962160757003
2000	27.060842011514776
2001	28.053770999215295
2002	27.56867460667695
2003	27.20039157604326
2004	26.990072780841473
2005	26.87200926589519
2006	25.840750474075698
2007	25.56821597041894
2008	26.81146851725867
2009	27.430463278027293
2010	29.153939570510104
2011	29.898737934436756
2012	30.690407076377344
2013	31.100898543369848
2014	31.742052534716276