The frequency of visiting a doctor: Is the decision to go independent of the frequency?
复现并扩展了Winkelmann对德国医疗改革的研究，分析患者是否去看医生与看医生次数之间的相关性，发现零相关源于模型设定问题，但支持其核心结论。
In his analysis of the effects of the reform of the German healthcare system, Winkelmann (Journal of Applied Econometrics 2004; 19: 455-472) investigates the number of doctor visits. He makes a distinction between the decision to go to a physician and the number of times the physician is visited in the observed time period. Winkelmann finds that there is no correlation between both decisions. This result appears to be far from straightforward since the primary driving force in both decisions will be the health of the patient. From this perspective a significant correlation is expected. In this paper, I first replicate part of Winkelmann’s research. I then set out to analyse whether the zero correlation is actually true or comes from the way the relation between both decisions is modelled. My empirical analysis confirms the latter, but nevertheless also corroborates Winkelmann’s main conclusions on the relevance of the explanatory variables used in his investigation.