Published online by Cambridge University Press: 11 February 2009
Excellent solutions have been proposed independently by Badi H. Baltagi and Qi Li (the posers of the problem), Juan J. Dolado, Ruud H. Koning, Essie Maasoumi, and Klaus Pötzelberger.
In the solution proposed by Essie Maasoumi, which is almost identical to the one proposed by Badi H. Baltagi and Qi Li, he provides an alternative solution to the second question by noting that
where ∂α/∂x = bαbx log α, has been used. Since log ρ < 0, the right-hand side of the above equation is positive if τ > 1 – ρ2, and is negative otherwise.
In his solution, Klaus Pötzelberger notes that the results do not depend on the assumption that u 0 is normally distributed. The problem could be solved for any distribution for u 0 with finite second moment.