SLIDE 96 Proof.
Consider all final transitions. We define transitions to be final when they lead to final states. A state s is defined as final if Ω(t, s) = {s} for all t. No choice is left to the agent but to remain in the current state. Recall that remaining in the current state involves no costs. For any final state ω ∈ Ω(t, s) we have: U(t′, ω | I(t, s)) = −Kt′,ω,s(Q(t′, ω, s)) + E[V (t′, ω) | I(t, s)] = −Kt′,ω,s(Q(t′, ω, s)) + E[(µt′,ω(X(t′, ω)) + p(t′, ω)) | I(t, s)] = −Kt′,ω,s(Q(t′, ω, s)) + µt′,ω(X(t′, ω)) + E[p(t, ω) | ∆[t′, ω | I(t, s)] > 0, I(t, s)] = −Kt′,ω,s(Q(t′, ω, s)) + µt′,ω(X(t′, ω)) + θ′αt,ω. Notice that µt′,ω(X(t′, ω)) + θ′αt,ω is known by Theorem 1 and due to the factor structure assumption. Thus we can identify the cost equation Kt′,ω,s(Q(t′, ω, s)). Imposing restrictions on the generality of the cost function Kt′,ω,s(Q(t′, ω, s)) is necessary such that U(t′, ω | I(t, s)) satisfies (ii), (v), and (iv). Standard arguments from Matzkin (1993) guarantee identification of the function Kt,s′,s(Q(t, s′, s)). We do not have to worry about the fact that only differences in utilities are identified in her setup as by (iii), we always have an alternative which implies zero costs. We can also identify the distribution FW (t′,ω,s)(w(t′, ω, s)) for any final states. Exploiting the factor structure we can then identify the joint distribution FW (t′,ω,s),P(t′,ω,s),E(j)(w(t′, ω, s), p(t′, ω, s), e(j)) for all final transitions and by isolating the dependency between unobservables, we identify the marginal distribution FH(t,ω,s)(η(t, ω, s)) for each final transition. Once these are obtained, by backward induction all expected value functions are identified and therefore all Kt,s′,s(Q(t, s′, s)) and FW (t′,ω,s),P(t′,ω,s),E(j)(w(t′, ω, s), p(t′, ω, s), e(j)) for any transition and all marginal distributions FH(t,ω,s)(η(t, ω, s)) for any transition are identified. Note that linearity does not fulfill the necessary conditions and only allows for identification up to scale. We therefore need to consider the case separately where the scale of the cost function is not identified. Heckman Estimation of Dynamic Discrete Choice Models