Models for which the MLE and the conditional MLE coincide

The MLE, CMLE and MMLE coincide in a linear regression model with fixed individual effects. In this case, there is no incidental parameters problem and the MLE is consistent. The equivalence of these estimators is important because CMLE=MLE implies both the consistency of the MLE and the efficiency of the CMLE. In general, we cannot expect to find a CMLE or MMLE, since there may be no fixed-dimension sufficient statistic for the effects, nor an appropriate transformation of the data whose distribution does not depend on the effects. However, we show that the MLE, CMLE and MMLE do coincide in systems of seemingly unrelated regressions and in systems of simultaneous equations. We establish this result for systems in which (exogenous) variables in addition to (or other than) the intercept may have coefficients which vary over individuals, provided that the set of such variables is the same in every equation.The financial support of the National Science Foundation is gratefully acknowledged.     

Economists and Data

This paper is concerned with one central question: the choice between theories, and the role played by data in that choice. It deals with the uses economists may make of data and the importance of understanding the institutional basis that gives rise to the data - an area in which labour economists have traditionally been particularly strong - and with the relevance of assumptions. It deals with the ultimate need to choose between competing theories (despite the role of conventionalism) on the basis of data rather than retreating into a comfortable 'methodological pluralism'. It considers the role of test replication, with reference to the practice in natural science (and its role there in checking scientific fraud) and concludes that, despite extensive technical problems of testing, economists have to accept a data check if the rhetoric of mathematical technicality is not to overwhelm the need to explain. Parallels are drawn with experience in physics (and the implications of the development of Chaos and Catastrophe for a naively predictionist view are noted), medicine and history (of which, it is argued, modern economists are far too neglectful).     

Racial differences in the feminization of poverty

The feminization of poverty refers to female householders and their children becoming an increasing percentage of the poor population. After examining effects of race on poverty of female-headed households from 1959 to 1989, this study investigates statistical relationships among female poverty, economic and labor market conditions, and transfer payments (specifically AFDC) by means of the Granger causality test over the period from 1966 to 1988. This study reinforces the plausible assumption that policies which would lower the unemployment rate of females and would increase real economic growth could be expected to reduce the number of poor female households.     

Another Look at the Cross-section of Expected Stock Returns

Our examination of the cross-section of expected returns reveals economically and statistically significant compensation (about 6 to 9 percent per annum) for beta risk when betas are estimated from time-series regressions of annual portfolio returns on the annual return on the equally weighted market index. The relation between book-to-market equity and returns is weaker and less consistent than that in Fama and French (1992). We conjecture that past book-to-market results using COMPUS-TAT data are affected by a selection bias and provide indirect evidence.     

On optimality in intergenerational risk sharing

Summary. This paper defines and studies optimality in a dynamic stochastic economy with finitely lived agents, and investigates the optimality properties of an equilibrium with or without sequentially complete markets. Various Pareto optimality concepts are considered, including interim and ex ante optimality. We show that, at an equilibrium with a productive asset (land) and sequentially complete markets, the intervention of a government may be justified, but only to improve risk sharing between generations. If markets are incomplete, constrained interim optimality is investigated in two-period lived OLG economies. We extend the optimality properties of an equilibrium with land and give conditions under which introducing a pay-as-you-go system at an equilibrium would not lead to any Pareto improvement. Received: October 5, 1998; revised version: April 3, 2001     

Länger leben — Siechtum und Pflege ohne Grenzen?

At present, our society and its social security system are not prepared to cope with the challenges resulting from the continuous increase of life expectancy. The traditional concept of disease has to be modified for serving the special needs of the elderly. The optimistic compression of disease theory is an intriguing model, but lacks prove by available data. The anti-aging boom diverts the focus from the social and financial burden that will be unevitably caused by long-term care in the future. If there will not be an — up to now unforeseeable — breakthrough in research, particularly dementia will have an enormous impact on social cost which is often underestimated.     

Efficient Liability Rules: Complete Characterization

Received May, 18, 2000; revised version received March, 19, 2001     

Exchange rate exposure and foreign exchange derivatives: do ineffective hedgers modify future derivatives use?

Recent studies examining the relationship between stock returns and exchange rate changes have provided evidence that the exchange rate exposure of non-financial companies is reduced by the use of foreign exchange derivatives. Building on such research, this study investigates whether past ineffective derivative hedging contributes to explaining future derivatives use. To the extent that companies monitor the effectiveness of their currency risk management practices, past ineffective hedgers can be expected to modify their future use of foreign exchange derivatives accordingly. In our study of 94 non-financial US multinationals, we provide evidence that the change in derivatives use from 1996–1998 to 1998–2000 can be explained in part by the ineffective hedging of currency risk in 1996–1998, controlling for variables associated with theories of optimal hedging. Additional analyses confirm that such primary results are robust to firm size, the level of foreign operations, and the use of derivatives to partially hedge currency risk. Our results imply that as exchange markets and risk management practices change, the use of derivatives to manage exchange rate risk also changes. Our contribution to this field of study is that we find evidence that past ineffective hedgers tend to increase their future use of FXDs.