Year	% of total
1971	3.8830632236994114
1972	3.614611521019883
1973	3.4589475526050433
1974	3.325027646451288
1975	3.415359848379943
1976	3.408946430069281
1977	3.000647137705263
1978	2.8194367490603236
1979	2.83803814396495
1980	3.3615360276989747
1981	4.161435368180331
1982	4.470503779955472
1983	4.428822704992964
1984	4.456756992654514
1985	4.056427519601738
1986	3.8580006675895153
1987	3.9631007482744263
1988	3.8287333118987092
1989	3.8322493615601383
1990	24.463449921305216
1991	23.457179015912047
1992	22.026607278914934
1993	21.017880368397652
1994	18.63405317692904
1995	18.06517065794779
1996	18.36612945920789
1997	18.43855204069358
1998	18.25281566710722
1999	18.31513886094892
2000	18.458250078144893
2001	18.739892352303364
2002	18.236503618659956
2003	17.978133552237438
2004	17.50565488463877
2005	17.009039904756463
2006	16.509786241075375
2007	15.915446784074788
2008	16.06659479961592
2009	15.701436428338742
2010	16.17661960923437
2011	14.79972551193866
2012	15.004030854951866
2013	14.678451247863212
2014	14.774151949659586
2015	15.039319481314436