What is the impact of duplicate coverage on the demand for health care in Germany?

Duplicate coverage involves those individuals who hold public health insurance, and purchase additional private coverage. Using data from the German Institute for Economic Research, we try to investigate the impact of duplicate coverage on the demand for healthcare (measured in number of visits to doctors). Given the simultaneity of the choices to take out additional private health insurance coverage, we estimate a negative binomial model to measure this impact. We also estimate a a Full Information Maximun Loglikelihood (FIML), known as Endogenous Switching Poisson Count Model and we compare these results with the standard maximum log likelihood (ML) estimators of the negative binomial model. The Results show that, there is a positive difference on the level of health services demanded when there is a duplicate coverage. We found also that there is evidence to think that in Germany there is a feedback between duplicate coverage and the demand of health services.Health care services demand, health insurance

Is it possible to accommodate massive photons in the framework of a gauge-invariant electrodynamics?

The construction of an alternative electromagnetic theory that preserves Lorentz and gauge symmetries, is considered. We start off by building up Maxwell electrodynamics in (3+1)D from the assumption that the associated Lagrangian is a gauge-invariant functional that depends on the electron and photon fields and their first derivatives only. In this scenario, as well-known, it is not possible to set up a Lorentz invariant gauge theory containing a massive photon. We show nevertheless that there exist two radically different electrodynamics, namely, the Chern-Simons and the Podolsky formulations, in which this problem can be overcome. The former is only valid in odd space-time dimensions, while the latter requires the presence of higher-order derivatives of the gauge field in the Lagrangian. This theory, usually known as Podolsky electrodynamics, is simultaneously gauge and Lorentz invariant; in addition, it contains a massive photon. Therefore, a massive photon, unlike the popular belief, can be adequately accommodated within the context of a gauge-invariant electrodynamics.Comment: 10 page