Year	% of total
1990	23.910639836666686
1991	24.18205675326805
1992	24.0745759566214
1993	24.401022310493918
1994	24.359631851340268
1995	24.06557321896238
1996	24.08796159749822
1997	23.95946995298838
1998	23.706234200428508
1999	23.48720358501253
2000	23.736332332520945
2001	24.398677425787803
2002	24.945596354517242
2003	25.756734945031962
2004	26.19060247370047
2005	26.459325347295337
2006	26.71380909069046
2007	26.78605523114545
2008	27.05736459979532