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- Michael Schemper, Samo Wakounig, Georg Heinze
- Statistics in medicine
- 2009

Often the effect of at least one of the prognostic factors in a Cox regression model changes over time, which violates the proportional hazards assumption of this model. As a consequence, the average hazard ratio for such a prognostic factor is under- or overestimated. While there are several methods to appropriately cope with non-proportional hazards, in… (More)

- D Bonderman, H Wilkens, +10 authors I M Lang
- The European respiratory journal
- 2006

Chronic thromboembolic pulmonary hypertension (CTEPH) is characterised by nonresolving pulmonary thromboemboli that can be treated by surgical pulmonary endarterectomy (PEA). The authors of the present study sought to confirm known and to identify novel CTEPH risk factors in a controlled retrospective cohort study of prevalent CTEPH cases collected in three… (More)

- Samo Wakounig, Georg Heinze, Michael Schemper
- Statistical methods in medical research
- 2015

We extend the Tarone and Ware scheme of weighted log-rank tests to cover the associated weighted Mantel-Haenszel estimators of relative risk. Weighting functions previously employed are critically reviewed. The notion of an average hazard ratio is defined and its connection to the effect size measure P(Y > X) is emphasized. The connection makes estimation… (More)

- Gregor Lindner, Edith Doberer, +5 authors Wilfred Druml
- Wiener klinische Wochenschrift
- 2009

HINTERGRUND: Eine Einschränkung der Nierenfunktion geht mit einer verschlechterten Prognose bei Patienten mit Kardiomyopathie (CMP) einher; sogar geringe Anstiege des Serum-Kreatinins sind mit einer erhöhten Mortalität assoziiert. Dennoch gibt es kaum Daten zu prognostischen Faktoren bzw. zur Prognose von Patienten mit CMP, welche durch ein (sub-)akutes… (More)

- Michael Schemper, Alexandra Kaider, Samo Wakounig, Georg Heinze
- Statistics in medicine
- 2013

The analysis of correlations within pairs of survival times is of interest to many research topics in medicine, such as the correlation of survival-type endpoints of twins, the correlation of times till failure in paired organs, or the correlation of survival time with a surrogate endpoint. The dependence of such times is assumed monotonic and thus… (More)

- Philipp Pluch, Samo Wakounig
- ArXiv
- 2007

The aim of this technical report is to give a short overview of known techniques for network tomography (introduced in the paper of Vardi (1996)), extended by a Bayesian approach originating Tebaldi and West (1998). Since the studies of A.K. Erlang (1878-1929) on telephone networks in the last millennium, lots of needs are seen in todays applications of… (More)

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