Year	% of total
1970	30.059214513217096
1971	29.490615996075903
1972	28.774496609681034
1973	26.63529650559184
1974	24.460010451311877
1975	21.005759585274937
1976	17.334235407996303
1977	18.722551123645562
1978	23.192377472727415
1979	22.249808494484473
1980	23.4595106072319
1981	23.088745176109292
1982	23.041672520888497
1983	21.70445428745471
1984	21.259435465787405
1985	21.2127926999461
1986	21.73005961068854
1987	22.22112996168786
1988	22.119695908516064
1989	22.37364148474178
1990	14.049586776859504
1991	15.079365079365079
1992	14.728682170542637
1993	14.285714285714285
1994	13.970588235294118
1995	12.080536912751679
1996	12.121212121212121
1997	11.235955056179774
1998	10.362694300518134
1999	9.66183574879227
2000	9.049773755656108
2001	8.444444444444445
2002	8.695652173913043
2003	8.51063829787234
2004	8.368200836820083
2005	8.60655737704918
2006	8.4
2007	7.874015748031496
2008	8.076923076923077