Year	% of total
1970	22.2496241893415
1971	22.373416521399594
1972	22.097226610003613
1973	24.052614716387176
1974	25.259787851236926
1975	26.69808082728226
1976	26.434038703332956
1977	27.198552110312193
1978	27.124352577092907
1979	27.406679487547734
1980	28.364081696624545
1981	29.811265800440058
1982	29.69295986885532
1983	28.599991056669193
1984	29.72445078260147
1985	30.457903612476144
1986	32.01182736443287
1987	32.374381450737786
1988	32.88283944549879
1989	30.379644148186085
1990	33.04765169694892
1991	29.204152249134946
1992	24.5930644019816
1993	21.007194244604317
1994	18.076644974692694
1995	16.186656944950784
1996	15.601570867547304
1997	15.64265536723164
1998	15.627347858752819
1999	16.855631141345427
2000	17.82065834279228
2001	17.85449146250928
2002	18.322866642039155
2003	18.828297715549006
2004	20.684410646387832
2005	21.233913701741105
2006	21.768707482993197
2007	23.14744079449962
2008	23.42376767290791