Year	% of total
1970	10.777407657870972
1971	10.770739487030905
1972	11.065776194889573
1973	11.001666609718438
1974	11.406210340789153
1975	11.806917232064993
1976	11.852853824588614
1977	11.664057956425845
1978	11.403357152343442
1979	11.466386028432272
1980	11.74871258653744
1981	12.140345352440665
1982	12.290391314808701
1983	12.336333002704453
1984	12.681049750927617
1985	12.723065049269733
1986	13.887536875318718
1987	15.292049484338108
1988	16.474952756677965
1989	17.373774183254532
1990	12.6583004935532
1991	12.814788186101072
1992	12.99056833736476
1993	13.142857142857142
1994	13.311270454127596
1995	13.200602005476073
1996	13.054178407104896
1997	12.968314947309063
1998	12.816781860070328
1999	12.727334941572996
2000	12.696715049656227
2001	13.13939801580629
2002	13.827855918831332
2003	14.176872566874405
2004	14.543625931543891
2005	14.73850264797257
2006	14.930863884308005
2007	15.048679585679182
2008	15.27404104850488