Increasing the credibility of the twin birth instrument

Twin births are an important instrument for the endogenous fertility decision. However, twin births are not exogenous either as dizygotic twinning is correlated with maternal characteristics. Following the medical literature, we assume that monozygotic twins are exogenous, and construct a new instrument, which corrects for the selection although monozygotic twinning is usually unobserved in survey and administrative datasets. Using administrative data from Sweden, we show that the usual twin instrument is related to observed and unobserved determinants of economic outcomes, while our new instrument is not. In our applications we find that the classical twin instrument underestimates the negative effect of fertility on labor income. This finding is in line with the observation that high earners are more likely to delay childbearing and hence have a higher risk to get dizygotic twins.     

Duration of maternity leave in Germany: A case study of nonparametric hazard models and penalized splines

The paper investigates maternity leave behavior in West Germany for females being employed between 1995 and 2006 using data from the German Socio Economic Panel. The observational study focuses on the investigation of individual and family-related covariate effects on the duration of maternity leave following first or second childbirth, respectively. Dynamic duration time models are used in which covariate effects are allowed to vary smoothly with duration of being in maternity leave. The intention of the paper is to demonstrate with state of the art models how effects of covariables change over time and to analyse substantial differences between maternity leaves following first and second childbirth. Particularly the personal income of mothers and the educational attainment influence the decision when to return into employment. The leave period following second birth is influenced by the mothers' attachment to the labour market between their two maternity leave periods. As fitting routine penalized spline smoothing effects is employed using available software in R (http://www.r-project.org).     

Simple aggregation and disaggregation subject to minimal information loss and other criteria

The main purpose of this paper is to develop a method and an algorithm for the aggregation as well as disaggregation of n-way tables, thereby minimizing a set of suitable criteria. One should observe that there is no real difference between aggregation and disaggregation when using this method. Here are presented some basic facts about a mainly one-dimensional method and an outline showing how the method may be extended to more complex cases.     

酒店“形象屏蔽”创新理论与实证研究——以开封开元名都大酒店为例

迄今为止,已有41家国际酒店管理集团、67个品牌抢滩中国酒店市场,加之现阶段受国际金融危机、甲型H1N1流感等诸多因素影响,酒店业的竞争已达到白热化的程度。提出了酒店的＂形象屏蔽＂观点,对酒店＂形象屏蔽＂的影响因素、作用机制进行了深入探究,试图找出规避＂形象屏蔽＂现象的有效策略,同时将这一理论运用于开封开元名都大酒店,对酒店的＂形象屏蔽＂现象进行剖析,找到规避策略,降低客房空置率。