Year	% of total
1971	31.387750328469714
1972	33.61254647653864
1973	33.22603105602701
1974	35.891509219477655
1975	35.48303397161684
1976	37.02199158427426
1977	36.639208184755205
1978	36.4496986886481
1979	36.46336252510745
1980	35.693475664747154
1981	34.916894219655184
1982	33.416728662833364
1983	31.4941239566773
1984	31.244258575480604
1985	30.595808105936584
1986	29.775709495055462
1987	27.635336049624833
1988	27.460042486148495
1989	27.43081208670835
1990	40.26147397986069
1991	40.53352425712695
1992	40.308833135368175
1993	40.39387173614864
1994	41.002903617622636
1995	38.69433143916381
1996	38.02086182740862
1997	36.58884381459629
1998	36.14610670111523
1999	36.104318807227045
2000	35.2949526210292
2001	35.1756936882322
2002	35.02769176091201
2003	36.29229179403493
2004	35.2767778601027
2005	35.51107823448486
2006	34.64648976602977
2007	33.45245374099063
2008	33.86099024849744
2009	33.142935417807166
2010	34.70289091250847
2011	34.532345518041815
2012	34.84849573212939
2013	34.870885506221285
2014	34.88346509636005
2015	33.20133323869022