Year	% of total
1971	1.132195736197734
1972	1.0743011701843843
1973	1.692986662372314
1974	2.3673071273964292
1975	2.695812753054489
1976	3.2763934679158044
1977	4.48332544720354
1978	5.9048278284085365
1979	7.056501418836122
1980	7.757194217256077
1981	7.713206217674406
1982	8.135202885450381
1983	8.526845470463297
1984	10.719836140746473
1985	10.825748426056562
1986	10.62564725713229
1987	11.06545567737861
1988	10.919864632164979
1989	10.885080501717749
1990	10.984670692223933
1991	11.116629608787836
1992	11.078949510809071
1993	11.301729407141368
1994	11.987954158902143
1995	12.106800249330146
1996	12.713949683575235
1997	13.667899140932363
1998	13.768275895278196
1999	14.274312806605884
2000	13.83361429436201
2001	13.846360255228396
2002	14.200694207424178
2003	14.002358339696045
2004	13.433844093348144
2005	12.59709515033479
2006	12.673528563823409
2007	12.813594178755627
2008	12.768728049273967
2009	13.022183485897711
2010	13.43909974803388
2011	13.50475712758622
2012	13.566674321944664
2013	13.488174067988023
2014	13.636644256626147
2015	13.518413790287157