Year	% of total
1970	7.240390234167618
1971	7.059703865545024
1972	7.176299519137534
1973	6.742589236383038
1974	6.946528460033107
1975	7.182155316303593
1976	7.489861026974004
1977	7.646677633209395
1978	7.661365139982503
1979	7.785717512397255
1980	7.9671586753606345
1981	8.025423237905292
1982	8.449059160771274
1983	8.647742594908168
1984	8.78865644085486
1985	8.619690981806084
1986	8.629608963492606
1987	8.77026582481433
1988	8.74822011414368
1989	8.691103132664797
1990	6.510814944286651
1991	6.571367612545338
1992	7.0322865988500665
1993	7.05528070552807
1994	6.764058435061036
1995	6.8691950464396285
1996	6.888888888888889
1997	7.191844300278036
1998	8.280515232058884
1999	7.490237841675541
2000	7.6775096187478145
2001	7.855662983425414
2002	8.082191780821917
2003	8.316291751874575
2004	8.366533864541832
2005	8.655126498002662
2006	8.26201448321264
2007	7.82285437207047
2008	7.3424917100900045