Year	% of total
1971	26.7028525213198
1972	26.16643375939803
1973	26.233683316349016
1974	26.568998433946987
1975	26.712108780555937
1976	27.553660061593433
1977	27.820157745307217
1978	28.62008176653256
1979	27.713598045537914
1980	26.70510740245127
1981	26.846217609732157
1982	25.24421266148155
1983	23.729902039585202
1984	23.73038256140515
1985	22.912407214693022
1986	23.009947943935895
1987	22.35939069940263
1988	23.322433572163472
1989	22.161687941287635
1990	24.54103728634045
1991	23.997845311114688
1992	23.696324103611385
1993	23.77828692600417
1994	23.426065110122657
1995	22.499993038188173
1996	21.96746597183294
1997	21.24811600433101
1998	20.727277049225762
1999	19.89896177179311
2000	18.88780301068323
2001	17.934633699165616
2002	17.468018124386223
2003	17.307689315649398
2004	17.84586511480913
2005	18.296177348870383
2006	18.663233317831118
2007	17.282952751864055
2008	16.700745108485428
2009	15.746584488341227
2010	16.129019258255724
2011	16.31057831960006
2012	15.342183718923566
2013	15.754708022792949
2014	14.643188309134846
2015	13.969310646017133