Year	% of total
1970	18.98602114898861
1971	19.36452803731248
1972	19.290049031276858
1973	18.61448994345484
1974	23.173630388009574
1975	22.494934596709587
1976	22.425304767175255
1977	20.017615675377982
1978	22.57127172601259
1979	21.991003284715045
1980	19.475916650232513
1981	22.090222710914663
1982	21.517545978547258
1983	23.914005738631968
1984	24.26812404655253
1985	25.83083272852575
1986	25.746277558767154
1987	25.218897674921735
1988	26.936855003286087
1989	25.478386656685714
1990	29.01023890784983
1991	30.4
1992	32.863849765258216
1993	35.46944858420268
1994	36.66191155492154
1995	37.87465940054496
1996	37.4025974025974
1997	35.851318944844124
1998	34.033149171270715
1999	37.48558246828143
2000	34.95850622406639
2001	40.618556701030926
2002	40.86345381526104
2003	39.69754253308129
2004	40.991420400381315
2005	37.954939341421145
2006	39.198606271777
2007	40.81455805892548
2008	41.344537815126046