The genetic epidemiology group at the University of Leicester
is offering the following MRC-funded PhD project to work with
Professors John Thompson and Paul Burton on the following topic:
Modelling non-random ascertainment in genetic family data
Brief Description:
Studies of the genetics of complex diseases, such as asthma and
ischaemic heart disease, often rely on recruiting families of
subjects. It is rarely possible to recruit families at random,
however other methods of sampling can lead to a severe form of
selection bias known as ascertainment bias. For instance,
ascertainment bias arises if families are only sampled when at
least one member is affected and so at-risk families with no
affected members are unobserved. Statistical models for
addressing the problems of ascertainment bias involve
high-dimensional integration and are very difficult to
implement fully even using the latest Markov Chain Monte Carlo
(MCMC) methods. To compound the problem, published work from
the Genetic Epidemiology Group in Leicester has demonstrated
that some modified MCMC approaches that are practical, do
not produce full adjustment for the bias. This PhD project
would build on this work in order to understand better why
practical MCMC methods sometimes fail and then to develop
improved methods for adjusting for the ascertainment bias.
The problem will be tackled from two complementary directions:
(a) fitting conventional models by maximum likelihood or
MCMC methods that simulate pseudo-observations to reflect
the unobserved families; (b) post-processing the estimated
parameters from approximate MCMC analyses to improve the
adjustment for ascertainment bias. Real and simulated
data sets will be used to assess the performance of the
various approaches.
The stipend is the usual £12,000 tax-free per annum. Knowledge of
genetics is not essential if the candidate has a good background in
Mathematics/Statistics and is interested in biological applications.
The topic is also suitable for a numerate biologist who perhaps
has a Master's Degree with a substantial statistics component.
However, these are only rough guidelines and we would encourage
anyone who is at all interested to contact John Thompson at
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Nuala A. Sheehan,
Department of Epidemiology and Public Health,
University of Leicester,
22-28 Princess Road West,
Leicester LE1 6TP, UK
Tel: +44 (0)116 2525456
Fax: +44 (0)116 2523272
Email: [log in to unmask]
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