Publications

"Semiparametric Count Data Modeling with an Application to Health Service Demand" (with Philipp Bach and Martin Spindler), Econometrics and Statistics, 2018, 8, 125-140

Heterogeneous effects are prevalent in many economic settings. As the functional form between outcomes and regressors is generally unknown a priori, a…

"Heterogeneous Effects of a Nonlinear Price Schedule for Outpatient Care" (with Peter Ihle, Ingrid Schubert, Joachim Winter and Amelie Wuppermann), Health Economics, 2017, 26(10), 1234-1248

Nonlinear price schedules generally have heterogeneous effects on health-care demand. We develop and apply a finite mixture bivariate probit model to…

"Testing under a Special Form of Heteroscedasticity" (with Heinrich Kögel), Applied Economics Letters, 2017, 24(4), 264-268

In the presence of heteroscedasticity, conventional standard errors (which assume homoscedasticity) can be biased up or down. The most common form of…

"The Many Weak Instrument Problem and Mendelian Randomization" (with Stephen Burgess, Neil Davies, Stephanie von Hinke Kessler Scholder, George Davey Smith and Frank Windmeijer), Statistics in Medicine, 2015, 34(3), 454-468

Instrumental variable estimates of causal effects can be biased when using many instruments that are only weakly associated with the exposure. We…

"Extensions of Hurdle Models for Overdispersed Count Data", Health Economics, 2013, 22(11), 1398-1404

Hurdle models are frequently used to model count data. Recent developments in the count data literature make it possible to relax commonly imposed…

"Per-period Co-payments and the Demand for Health Care: Evidence from Survey and Claims Data" (with Joachim Winter), Health Economics, 2013, 22(9), 1111-1123

When health insurance reforms involve non-linear price schedules tied to payment periods (for example, fees levied by quarter or year), the empirical…

"GMM with Many Weak Moment Conditions: Replication and Application of Newey and Windmeijer (2009)", Journal of Applied Econometrics, 2012, 27(2), 343-346

In a recent article Newey and Windmeijer (Generalized method of moments with many weak moment conditions. Econometrica 2009; 77(3): 687-719) propose a…

"Estimation of Hurdle Models for Overdispersed Count Data", Stata Journal, 2011, 11(1), 82-94

Hurdle models based on the zero-truncated Poisson-lognormal distribution are rarely used in applied work, although they incorporate some advantages…