As part of a study on how children affect parents' depression in old age, researchers fit a model for total number of children in a family (Social Science & Medicine, Jan. 2014). One of the key independent variables used in the model is whether the first birth was a single birth or a multiple (twin, triplet) birth.
a. Create a dummy variable for type of first birth.
b. Write a model for total number of children (y) as a function of type of first birth.
c. Give a practical interpretation of each of the β-coefficients in the model.