There is a unidimensional scale with four items, which can be represented in a factor analysis model as follows: X1 = a1 F + E1 X2 = a2 F + E2 X3 = a3 F + E3 X4 = a4 F + E4 Assuming the total score X = X1 + X2 + X3 + X4, and Var(F) = 1. Express the reliability of X in terms of a1, a2, a3, a4, Var(X). (Hint: a1F represents T1 in CTT)