According to a Caltech/MIT survey of both registered and unregistered eligible voters who did not cast a ballot in 2008, disapproval of candidate choices, busyness, illness, transportation, and registration/ administrative problems were the leading causes of non-participation, with considerable variation across groups...
...Taken together, the surveys suggest that white citizens who abstain from voting do so primarily by choice, while the majority of minority non-voters face problems along the way.