Statistics (S3RI) Seminar - Multivariable Modelling of Continuous Covariates with a Spike at Zero, Dr Carolin Jenkner (University of Freiburg) Seminar
- Time:
- 14:00 - 15:00
- Date:
- 1 November 2018
- Venue:
- Room 7035, Lecture Theatre 7B, Building 54, Mathematical Sciences, University of Southampton, Highfield Campus, SO17 1BJ
For more information regarding this seminar, please email Dr Helen Ogden at H.E.Ogden@southampton.ac.uk .
Event details
In a lot of clinical and epidemiological studies, covariates with a large amount of observations with value zero occur. One simple example is the covariate "cigarettes smoked per day''. Here non-smokers take value zero, so that in studies investigating the effect of this covariate the amount of zeros will be relatively high. Covariates with a spike at zero (SAZ) are continuous covariates with this special distribution. The proportion of observations with value zero is higher than for continuous covariates with standard distributions (e.g. normal distribution etc.). In this talk the properties of these covariates as predictor variables in statistical models is investigated and how their effect on different outcomes can be modelled appropriately.
For analysing the effect of two covariates with SAZ on an outcome variable, four modelling strategies including different binary indicator covariates are proposed. All four methods are extensions of a non-linear modelling technique for one covariate with SAZ based on fractional polynomials (FPs) with inclusion of a binary variable indicating if the covariate is zero or not (FP-spike). Results of a simulation study, in which the four methods are investigated and compared to standard linear regression and FP as non-linear modelling technique will be presented. For illustration, application to data of a study on laryngeal cancer is presented.
Speaker information
Dr Carolin Jenkner, University of Freiburg. Carolin Jenkner currently works at the Clinical Trials Unit, University Medical Center Freiburg.