Year	% of total
1970	95.51759099266812
1971	95.97462813882869
1972	96.73117097208821
1973	97.32527277807263
1974	97.19262415222114
1975	96.20645061697064
1976	96.73856477589078
1977	96.67937480534944
1978	95.9647919173302
1979	95.97033434186893
1980	96.20632417229754
1981	95.29635158542217
1982	93.48206666531883
1983	91.19530334202622
1984	85.8807404274537
1985	82.91738334956757
1986	84.92644586665287
1987	83.558960166956
1988	85.50179139816393
1989	85.56045052530085
1990	11.282051282051283
1991	13.642891335567256
1992	15.657245401525346
1993	17.49788672865596
1994	19.081836327345307
1995	20.575975748389542
1996	21.92571222502705
1997	23.132530120481928
1998	24.33146252888742
1999	25.492689129052764
2000	26.354230066950702
2001	29.156908665105384
2002	31.780976573525262
2003	34.19618528610354
2004	36.323105166535534
2005	38.41277890466531
2006	40.54187192118226
2007	42.420625447600855
2008	44.47552447552447