The outside investor receives share (1-α) of the returns from the funds that are actually invested in the firm. The expected value of the equity in the firm is therefore
π= R(I – k(1-αR)),
Where π is the equity value of the firm. This is the value of all the equity held by both outsiders and managers, which equals the total value of the firm minus the value of stealing.
Differentiating with respect to R gives the ”absoluteresponsiveness,”
ρa = ∂ π/∂R = I – k + 2Rkα,
which is the sensitivity of firm value to changes in R. This is always positive because we have assumed that the optimal level of stealing is less than I. The maximum value of stealing, given by the first-order condition when αR is zero, is k. We have already assumed that there cannot be “negative” stealing, so k ≤ I, and thus is sufficient to ensure that ρa > 0.