Year	% of total
1971	5.9353471118177
1972	11.041573535985695
1973	11.542857142857143
1974	6.558810668998688
1975	15.733256351039259
1976	18.704335119337554
1977	21.53617653299385
1978	29.460580912863072
1979	34.08728894552405
1980	43.49281629236992
1981	53.215020576131685
1982	51.78152836380685
1983	63.02077355675427
1984	53.90694568121104
1985	51.4431073280501
1986	43.82314694408323
1987	50.909897913892586
1988	46.29311824266346
1989	50.12097088894092
1990	53.65074649038104
1991	46.43184866238441
1992	44.68113792638533
1993	48.12133746983799
1994	53.17751593587019
1995	46.23194803556789
1996	45.74278150587946
1997	65.29751194391015
1998	61.78280722652373
1999	61.78755671576853
2000	61.784477490323894
2001	61.78372784891993
2002	61.78231608261777
2003	63.09948474038842
2004	66.59938208032956
2005	66.99944772505204
2006	72.8991778450887
2007	72.90016537557665
2008	72.89909995262909
2009	77.09966122263235
2010	75.59817771141994
2011	78.23851446326847
2012	80.28635128544556
2013	81.56008724855451
2014	82.40868706811452
2015	81.80487494431362