Year	% of total
1971	31.004593284401334
1972	34.00011462489899
1973	34.20333922937744
1974	36.633578899948645
1975	37.316760849479664
1976	38.39845213497227
1977	38.51336212744604
1978	37.313979327121125
1979	37.89385756280543
1980	39.005911490177795
1981	38.57640393340031
1982	36.9645396911599
1983	33.34772351947511
1984	32.551755106375175
1985	33.31283228395516
1986	32.52993237821789
1987	31.18356406950366
1988	29.88100173793754
1989	30.16468796183568
1990	52.5557661927394
1991	52.184890871881095
1992	51.09967111952071
1993	52.428008402051276
1994	51.4645888089731
1995	47.666206660995805
1996	47.09340611994104
1997	44.74660056021939
1998	43.516839863305826
1999	44.473895427609904
2000	44.50127265518422
2001	43.60713435881633
2002	41.45169178818418
2003	40.75406482557968
2004	39.975841268484494
2005	39.281218860291496
2006	37.92508371741635
2007	37.203239479585726
2008	35.57086473815853
2009	36.13687039373598
2010	36.43879615430027
2011	38.018383367849346
2012	37.915356505794726
2013	38.795031170024565
2014	39.11696639542341
2015	36.24376435488017