Year	% of total
1971	12.265514877728657
1972	11.764007965777564
1973	10.580346538404886
1974	10.538022523354169
1975	10.460500025361636
1976	9.879629770870432
1977	12.009408951147828
1978	11.837481664113875
1979	13.622835472115524
1980	16.071078550661447
1981	16.858659466188506
1982	16.42195121929745
1983	15.405359024636583
1984	14.324038010137047
1985	14.95102240991535
1986	13.970749340447346
1987	14.578936191683658
1988	14.121137871695923
1989	14.660521301521486
1990	49.25078718499453
1991	45.5944213025629
1992	44.64323733828003
1993	44.54188191293147
1994	42.50289502980835
1995	40.57608883104688
1996	39.3861308631074
1997	40.74071768118018
1998	41.89515429532802
1999	42.379404164692694
2000	43.55837459262005
2001	44.15221906632294
2002	45.306760511750355
2003	50.1766680553194
2004	50.90748963924747
2005	47.945616285260265
2006	44.923323956901115
2007	45.69694025796358
2008	42.410761668279875
2009	42.37413143184611
2010	41.755156082698406
2011	43.27605464322567
2012	43.135878455571266
2013	41.45525056674989
2014	41.961005810678664
2015	41.742979768194516