Year	% of total
1971	22.035588894117176
1972	24.275598250999593
1973	27.961008623521018
1974	28.158596949608338
1975	28.665314841314903
1976	32.46128650719623
1977	30.875908733752794
1978	33.22554023660456
1979	35.69473366734064
1980	43.335886356515005
1981	41.12712938136938
1982	38.77620603559142
1983	39.26138598752518
1984	41.374635805652986
1985	42.48597022701879
1986	42.329595411720554
1987	41.9967070057466
1988	43.0842957911022
1989	45.07901136514769
1990	47.77550406437956
1991	47.15335650668804
1992	48.23209128616845
1993	51.28902869571742
1994	51.745496668873244
1995	51.57174821784729
1996	51.89809763665304
1997	51.043292733910164
1998	49.025487257906335
1999	50.56353413792439
2000	50.91204070780053
2001	54.845508301715384
2002	55.395961003709715
2003	56.60126047008499
2004	57.71838322220717
2005	60.33194679903112
2006	61.246661534668355
2007	61.034354091061175
2008	61.40855188023229
2009	60.89905351893879
2010	61.544228973754855
2011	61.563415883980035
2012	61.1164381471862
2013	62.814548067807706
2014	61.37707551339654
2015	63.84730030451349