Year	% of total
1970	27.444412525896873
1971	28.437693965106103
1972	28.860726421147298
1973	27.673095719233064
1974	33.075573538968456
1975	31.03100315748045
1976	30.310865258921304
1977	26.83403120584406
1978	30.21602600697814
1979	28.904297564691
1980	25.022499140763117
1981	29.114177550490407
1982	25.715963788722334
1983	28.35660473273725
1984	28.494209592575224
1985	30.606368439639937
1986	30.161243583031723
1987	29.55399038674893
1988	29.94091856574203
1989	28.951748021892993
1990	35.467980295566505
1991	36.41025641025641
1992	37.634408602150536
1993	38.82978723404255
1994	39.79057591623037
1995	43.455497382198956
1996	40.72164948453608
1997	37.67441860465116
1998	36.0655737704918
1999	39.49579831932773
2000	39.130434782608695
2001	41.76706827309237
2002	40.44943820224719
2003	40.647482014388494
2004	43.38235294117647
2005	38.006230529595015
2006	40.53156146179402
2007	42.01388888888889
2008	40.13377926421405