Negative values for estimated variances can arise in a panel data context. Empirical and theoretical literature dismisses the problem as not serious and a practical solution is to replace negative variances by its boundary value, i.e. zero. While this is not a concern when the individual...

Within the framework of dynamic panel data models with mean stationarity, one additional moment condition may remarkably increase the efficiency of the system GMM estimator. This additional condition is essentially a condition of “homoskesdasticity” of the individual effects; it is...

One of the major virtues of panel data models is the possibility to control for unobserved and unobservable heterogeneity at the unit (individual, firm, sector...) level, even when this is correlated with the variables included on the right hand side of the equation. By assuming an additive...

This paper develops a new moment condition for estimation of linear panel data models. When added to the set of instruments devised by Anderson, Hsiao (1981, 1982) for the dynamic model, the proposed approach can outperform the GMM methods customarily employed for estimation. The proposal builds...

In a panel data model with random effects, when autocorrelation in the error is considered, (Gaussian) maximum likelihood estimation produces a dramatically large number of corner solutions: the variance of the random effect appears (incorrectly) to be zero, and a larger autocorrelation is...

This paper aims at characterizing the dynamics of R&D competition within the pharmaceutical domain, focusing on the role of patent disclosure, the extent of uncertainty, and role of scientific advances. Following the empirical literature in the economics of innovation, we employ patents as a...

During the last thirty years health care expenditure (HCE) has been growing much more rapidly than GDP in all OECD countries posing increasing concern on the long-term sustainability of current trends. Against this background, we look at the determinants of HCE in European countries, explicitly...

This paper aims at examining whether an increased stringency of Intellectual Property Right (IPR) protection is apt to stimulate international cooperation on research projects between developed and emerging countries. To address this issue, we look both at scientific and technological...

We analyze the decline of R&D productivity in pharmaceuticals and its determinants. Since the molecular biology revolution, science has dramatically expanded the set of plausible therapeutic targets. However, innovation has become more difficult to achieve, and attrition rates of R&D projects...