APOE and dementia: This model articulates two mechanisms by which low education causes dementia, splitting the sufficient cause with low education/Z1 (used in previous examples) into two sufficient causes: in one, low education and Z1a are sufficient to produce dementia (i.e., in some individuals, low education does not have to work with APOE ε4 to cause dementia) and in the other, low education along with the modifier of interest APOE ε4 and Z1b are sufficient to produce dementia.