Year	% of total
1970	22.74029977359324
1971	22.74882889559172
1972	22.861718149854735
1973	23.33540616578707
1974	23.86351698157225
1975	23.339563282081556
1976	22.1678828459703
1977	21.971928732502736
1978	21.638961591706614
1979	20.95463289280463
1980	21.187151368806813
1981	22.503100006060038
1982	20.68850062340928
1983	17.94317296123983
1984	18.10821307538418
1985	17.922112872340627
1986	18.047748895078097
1987	17.317543926942562
1988	17.458379344541257
1989	19.104639389082863
1990	38.421366756192185
1991	37.68464996788696
1992	36.033657812242204
1993	34.20156622403813
1994	34.18921247630536
1995	33.632840028188866
1996	32.808868228142316
1997	33.494797273053464
1998	33.426808749298935
1999	32.41800152555302
2000	31.2390243902439
2001	29.046898638426626
2002	29.459933710274903
2003	29.21108742004264
2004	28.484729835552073
2005	28.804347826086957
2006	29.262628217534353
2007	29.764243614931235
2008	29.557137208382763