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Chris Theobald

BioSS Associate

Biomathematics & Statistics Scotland
JCMB, The King's Buildings,
EDINBURGH, EH9 3JZ, Scotland, UK.

Tel: +44 (0)131 650 4878
Fax: +44 (0)131 650 4901

Email: Chris Theobald

I had a joint appointment in BioSS and the School of Mathematics, University of Edinburgh from 2001 to 2011. I now contribute to external projects on potato trials, insect detection in salads and optimum nitrogen fertilization.

Research Interests

My main interest is in the application of Bayesian methods in agriculture. I argue that Bayesian procedures should replace conventional estimative approaches in order to make systematic use of expert knowledge. These are some applications of my ideas.

• Crop varieties for local environments With Mike Talbot of BioSS I have investigated the application of Bayesian decision theory to the selection of crop varieties best suited to local environments. Funding from the Home-Grown Cereals Authority (HGCA) has supported the development of computer-based tools to help farmers and advisors identify varieties best adapted to local circumstances: these are available at http://www.hgca.com/varieties/rl-plus/.
• Fertilizer optimization We have also used decision theory to find the optimum choice of variety and fertilizer level for cereals, taking account of crop yield and fertilizer cost. We have since extended our method to allow the value of the crop to depend on a quality measurement, such as grain nitrogen, and to include measurements of soil nitrogen.
• Seed rate optimization With Adrian Roberts of BioSS and funding from HGCA, I have investigated optimum seed rates for winter wheat, and how they should vary with sowing date and latitude over the UK.
• Predicting fungal contamination in wheat Contamination of wheat grain by bunt (Tilletia caries) is usually measured by microscopic counting of spores washed from a seed sample, but polymerase chain reaction (PCR) technology offers a quicker and more convenient alternative. A Bayesian calibration model developed with Adrian Roberts accounts for sampling variation in both methods, and bias, censoring and run-to-run variation in the PCR method.

I am also interested in the design and analysis of visual perception experiments. With Aletta Nonyane and the late Rob Kempton, I have investigated the construction and properties of designs for visual perception experiments which are balanced for carry-over effects. These designs are now being used in neuroimaging. See the DesignSequence Page for more information. We have also developed and applied a Bayesian predictive method for correcting bias in sequences of quantitative visual responses.

With Ayona Chatterjee and Graham Horgan of BioSS, I have considered Bayesian models for dietary data recorded on successive days, particularly components of diet which have very skewed distributions and large proportions of zeros, such as retinol, alcohol and pesticide residues. We have developed a multivariate latent-Gaussian model for the consumption of Iprodione, a widely used pesticide, combining information over several food products on which it is used.

Another interest is in multivariate analysis, particularly discriminant analysis and pattern recognition.

• Automated recognition of chromosomes and cereal seeds With Andrew Carothers of the MRC Human Genetics Unit and Simon Kirby I developed several discrimination methods for improving the speed and accuracy with which chromosomes could be recognised. I have since supervised research on the automated recognition of cereal seeds, in cooperation with the Scottish Agricultural Statistics Service and the Scottish Agricultural Science Agency.
• Automated segmentation of CT X-ray images With Chris Glasbey of BioSS and Caroline Robinson I worked on methods for automated segmentation of computed-tomography X-ray images of sheep.

Considering how to exploit the approximate bilateral symmetry of the X-ray images led us to investigate principal component analysis of landmarks from what we call reversible two-dimensional images.

Journal Publications from 2002

Journal Publications

Recent Papers

(available as pdf)

• Estimation of economically optimum seed rates for winter wheat from series of trials. J H Spink, M Talbot, C M Theobald and A M I Roberts (Journal of Agricultural Science 144 (2006), 303-316)
• Bayesian solutions to some decision problems in crop management and variety choice. C M Theobald (Plant Breeding Lecture Series, Iowa State University (2006))
• Assessment of expert opinion: seasonal sheep preference and plant response to grazing. M L Pollock, J P Holland, C M Theobald and C J Legg (Rangeland Ecology and Management, 60 (2007), 125-135)
• Calibration of quantitative PCR assays. A M I Roberts, C M Theobald, and M McNeil (Journal of Agricultural, Biological, and Environmental Statistics 12 (2007), 364-378)
• Design sequences for sensory studies: achieving balance for carry-over and position effects. B A S Nonyane and C M Theobald (British Journal of Mathematical and Statistical Psychology, 60 (2007), 339-349)
• Multiplicative models for combining information from several sensory experiments: a Bayesian analysis. B A S Nonyane and C M Theobald (Food Quality and Preference, 19 (2008), 260-266)
• Exposure assessment for pesticide intake from multiple food products: a Bayesian latent-variable approach. A Chatterjee, G W Horgan and C M Theobald (Risk Analysis 28(2008), 1727-1736)
• Group testing, the pooled hypergeometric distribution and estimating numbers of defectives in small populations C M Theobald and A M Davie (submitted to Communications in Statistics – Theory and Methods)
• A hierarchical Bayesian mixture model for repeated dietary records. C M Theobald, A Chatterjee and G W Horgan (Food and Chemical Toxicology 50 (2012) 320-327)