<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
</head>
<body text="#000000" bgcolor="#FFFFFF">
<p>Dear all,</p>
<p>On Thursday (1 November) at 2pm in <span class="event-where">54
/ 7035 (7B), we have an S3RI seminar from </span><span
class="event-where"><span class="event-description">Carolin
Jenkner, University of Freiburg</span> on </span><span
class="event-where"><span class="event-description">"</span></span><span
class="event-where"><span class="event-description"><span
class="event-description"><span class="event-description">Multivariable
modeling of continuous covariates with a spike at zero</span></span>".
Details are given below.<br>
</span></span></p>
<p><span class="event-where"><span class="event-description"><span><span
class="event-description">The seminar will also be
available via a live web-cast at</span></span></span></span><br>
<a class="moz-txt-link-freetext" href="https://coursecast.soton.ac.uk/Panopto/Pages/Viewer.aspx?id=c2bc1d87-ef9e-46a3-91a1-912ed9a8704e">https://coursecast.soton.ac.uk/Panopto/Pages/Viewer.aspx?id=c2bc1d87-ef9e-46a3-91a1-912ed9a8704e</a></p>
<p><span class="event-where"><span class="event-description"><span><span
class="event-description">The talk will be followed by tea
and cake in the staff reading room on level 4 of building
54. </span></span></span></span></p>
<p><span class="event-where"><span class="event-description"><span><span
class="event-description">All are welcome!</span></span></span></span></p>
<p><span class="event-where"><span class="event-description"><span>Best
wishes,</span></span></span></p>
<p><span class="event-where"><span class="event-description"><span>Helen</span></span></span></p>
<p><span class="event-description">Multivariable modeling of
continuous covariates with a spike at zero <br>
</span></p>
<p><span class="event-description">
Carolin Jenkner, University of Freiburg <br>
</span></p>
<p><span class="event-description">
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.</span></p>
<br>
<span class="event-where"><span class="event-description"><span><span
class="event-description"><span> <span
class="event-description"> </span><span
class="event-description"><span
class="event-description">For the current schedule of
S3RI seminars, see <a class="moz-txt-link-freetext"
href="https://tinyurl.com/s3riseminar">https://tinyurl.com/s3riseminar</a>
</span></span></span></span></span></span></span><br>
<p><span class="event-where"><span class="event-description"><span><span
class="event-description"></span></span></span></span></p>
</body>
</html>