Questions 1, 2, and 3 are based on the information given below:

In a hypotheticalstudy investigating the interaction between factor Aand factor B and the risk of disease X;

Incidence of disease in the absence of factor A and factor B = 2per 100,000 population

Incidence of diseaseif factor A is present and factorB absent = 14 per 100,000 population

Incidence of diseaseif factorB is present and factorA absent = 10 per 100,000 population

1.Using the additive model of interaction, what is the expected incidence in persons who are exposed to both factors A and B if those persons experienced the risk resulting from the independent contribution of both factors?

2.Using the multiplicative model of interaction, what is the expected incidence in persons who are exposed to both factors A and B if those people experienced the risk resulting from the independent contributions of both factors?

3.Suppose that the observed incidence for disease in the presence of both factors A and B is 40 per 100,000 population. Determine whether there is positive or negative interaction between factors A and B using:

a.additive model of interaction

b.multiplicative model of interaction

4.Describe an approach for evaluating whether a variable confounds an association.