In brief, the probit model for reading says that subject i read a book last year if Xiβ + Ui > 0.

(a) What are Xi and β?

(b) The Ui is a variable. Options (more than one may be right):

data random latent dummy observable

(c) What are the assumptions on Ui?

(d) The log likelihood function is a , with one for each . Fill in the blanks using the options below, and explain briefly.
sum product quotient matrix term subject factor entry book variable