ORCID Profile
0000-0003-4368-5145
Current Organisation
Australian National University
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Applied Statistics | Disease surveillance | Statistics | Statistical Theory | Sociology | Applied statistics | Biological mathematics | Sociological Methodology And Research Methods | Statistics | Human Geography Not Elsewhere Classified
Publisher: Scientific Societies
Date: 1992
Publisher: CSIRO Publishing
Date: 2011
DOI: 10.1071/CH11047
Abstract: To investigate O exchange during the reaction of POCl3 and water, natural abundance POCl3 was reacted with water highly enriched in 18O, and the resulting H3PO4 was isolated as KH2PO4. This reaction was conducted with and without tetrahydrofuran (THF) as a solvent, and was controlled in THF and violent in its absence. Approximately 5 × 10–4 M aqueous solutions of the KH2PO4 were analyzed using electrospray ionization mass spectrometry, to estimate the proportions of the mass-clumped 16,17,18O isotope analogues of [H2PO4]–. During analysis, ~29 % of [H2PO4]– dehydrated to [PO3]–, for which the proportions of the O isotope analogues were also measured. These proportions were compared with those predicted for O exchange at either four or three positions on the P atom of POCl3. The data strongly support O exchange at all four positions, whether or not THF was used to moderate conditions during the reaction. This result clears the way for safe, predictable synthesis of heavy-O labelled orthophosphate from POCl3 and 18O enriched water for evaluation as an environmental and biochemical tracer.
Publisher: Research Square Platform LLC
Date: 03-11-2022
DOI: 10.21203/RS.3.RS-2067234/V1
Abstract: Group-testing is an important element of biosecurity operations, designed to reduce the risk of introducing exotic pests and pathogens with imported agricultural products. Groups of units, such as seeds, are selected from a consignment, and tested for contamination, with a positive or negative test returned for each group. These schemes are usually designed such that the probability of detecting contamination is high assuming random mixing and a somewhat arbitrary design prevalence. We propose supplementing this approach with an assessment of the distribution of the number of contaminated units conditional on testing results. We develop beta-binomial models allowing for between-consignment variability in contamination levels, with a further layer of nesting to allow for possible clustering within the groups for testing. The latent beta distributions can be considered as priors and chosen based on expert judgement, or estimated from historical test results. We show that the parameter controlling within-group clustering is, unsurprisingly, effectively non-identifiable. It can be handled by sensitivity analysis, but we demonstrate theoretically and empirically that the probability of a consignment with contamination evading detection is almost perfectly robust to mis-specification of this clustering. We apply the new models to large cucurbit seed lots imported into Australia where they provide important new insights for biosecurity regulation.
Publisher: Wiley
Date: 09-03-2015
DOI: 10.1111/ANZS.12108
Publisher: Oxford University Press
Date: 19-01-2012
Publisher: Springer Science and Business Media LLC
Date: 03-12-2010
Publisher: Oxford University Press (OUP)
Date: 03-05-2017
Publisher: WHO Press
Date: 25-06-2018
Publisher: SAGE Publications
Date: 13-03-2017
Abstract: A binary health outcome may be regressed on covariates using a log link, rather than more typical link functions such as the logit. This allows the exponentiated regression coefficient for each covariate to be interpreted as a relative risk conditional on the remaining covariates. Relative risks are simpler to interpret than the odds ratios which arise with a logit link. There are practical and conceptual challenges in log-link binary regression, mainly due to the requirement that probabilities are less than or equal to 1. Viable probabilities are now usually achieved by the imposition of a constraint on the parameter space, but the log link function is still more work to apply in practice. We propose instead a new smooth link function which is equal to the log up to a cutoff and a linearly scaled logit function above the cutoff. The new approach is conceptually clearer, simpler to implement and generally less biased, and it retains the relative risk interpretation for all but the highest risk in iduals. Alternative binary regressions are compared using a simulation study and a diabetic retinopathy dataset.
Publisher: Cambridge University Press
Date: 28-08-2014
Publisher: Springer Science and Business Media LLC
Date: 12-2013
Publisher: Wiley
Date: 23-06-2016
DOI: 10.1111/INSR.12177
Publisher: Public Library of Science (PLoS)
Date: 11-06-2020
Publisher: MDPI AG
Date: 09-09-2023
DOI: 10.3390/ANI13182863
Publisher: Wiley
Date: 04-11-2018
Publisher: Wiley
Date: 20-09-2019
DOI: 10.1111/NPH.16117
Abstract: Although tannins have been an important focus of studies of plant–animal interactions, traditional tannin analyses cannot differentiate between the ersity of structures present in plants. This has limited our understanding of how different mixtures of these widespread secondary metabolites contribute to variation in biological activity. We used UPLC‐MS/MS to determine the concentration and broad composition of tannins and polyphenols in 628 eucalypt ( Eucalyptus , Corymbia and Angophora ) s les, and related these to three in vitro functional measures believed to influence herbivore defence: protein precipitation capacity, oxidative activity at high pH and capacity to reduce in vitro nitrogen (N) digestibility. Protein precipitation capacity was most strongly correlated with concentrations of procyanidin subunits in proanthocyanidins (PAs), and late‐eluting ellagitannins. Capacity to reduce in vitro N digestibility was affected most by the subunit composition and mean degree of polymerisation (mDP) of PAs. Finally, concentrations of ellagitannins and prodelphinidin subunits of PAs were the strongest determinants of oxidative activity. The results illustrate why measures of total tannins rarely correlate with animal feeding responses. However, they also confirm that the analytical techniques utilised here could allow researchers to understand how variation in tannins influence the ecology of in iduals and populations of herbivores, and, ultimately, other ecosystem processes.
Publisher: Wiley
Date: 03-2020
DOI: 10.1111/ANZS.12287
Publisher: Wiley
Date: 20-12-2009
DOI: 10.1002/SIM.3723
Abstract: Many health and other surveys aim to produce statistics on small subpopulations, such as specific ethnic groups or the indigenous population of a country. In most countries, there is no reliable s ling frame of the subpopulations of interest, hence it is necessary to s le from the general population, which can be very expensive. A range of issues and strategies for s ling rare subpopulations is reviewed. The most common approaches in practice are the use of a large screening s le, and disproportionate s ling by strata. Optimal s le designs have been derived for the case of one-stage s ling, but most household interview surveys use two or more stages of selection. This paper develops optimal designs for two-stage s ling, where there is auxiliary information on subpopulation numbers for each primary s ling unit. Various alternative designs are evaluated using a simulated population derived from the New Zealand Census.
Publisher: Oxford University Press (OUP)
Date: 10-2022
DOI: 10.1111/RSSA.12916
Abstract: S le designs are typically developed to estimate summary statistics such as means, proportions and prevalences. Analytical outputs may also be a priority but there are fewer methods and results on how to efficiently design s les for the fitting and estimation of statistical models. This paper develops a general approach for determining efficient s ling designs for probability-weighted maximum likelihood estimators and considers application to generalized linear models. We allow for non-ignorable s ling, including outcome-dependent s ling. The new designs have probabilities of selection closely related to influence statistics such as dfbeta and Cook's distance. The new approach is shown to perform well in a simulation based on data from the New Zealand Health Survey.
Publisher: Public Library of Science (PLoS)
Date: 07-03-2016
Publisher: Oxford University Press (OUP)
Date: 19-07-2006
DOI: 10.1111/J.1467-985X.2006.00434.X
Abstract: The number of people to select within selected households has significant consequences for the conduct and output of household surveys. The operational and data quality implications of this choice are carefully considered in many surveys, but the effect on statistical efficiency is not well understood. The usual approach is to select all people in each selected household, where operational and data quality concerns make this feasible. If not, one person is usually selected from each selected household. We find that this strategy is not always justified, and we develop intermediate designs between these two extremes. Current practices were developed when household survey field procedures needed to be simple and robust however, more complex designs are now feasible owing to the increasing use of computer-assisted interviewing. We develop more flexible designs by optimizing survey cost, based on a simple cost model, subject to a required variance for an estimator of population total. The innovation lies in the fact that household s le sizes are small integers, which creates challenges in both design and estimation. The new methods are evaluated empirically by using census and health survey data, showing considerable improvement over existing methods in some cases.
Publisher: Informa UK Limited
Date: 15-07-2010
Publisher: Springer Science and Business Media LLC
Date: 26-08-2023
DOI: 10.1007/S13253-023-00566-X
Abstract: Group testing is an important element of biosecurity operations, designed to efficiently reduce the risk of introducing exotic pests and pathogens with imported agricultural products. Groups of units, such as seeds, are selected from a consignment and tested for contamination, with a positive or negative test returned for each group. These schemes are usually designed such that the probability of detecting contamination is high assuming random mixing and a somewhat arbitrary design prevalence. We propose supplementing this approach with an assessment of the distribution of the number of contaminated units conditional on testing results. We develop beta-binomial models that allow for between-consignment variability in contamination levels, as well as including beta random effects to allow for possible clustering within the groups for testing. The latent beta distributions can be considered as priors and chosen based on expert judgement, or estimated from historical test results. We show that the parameter representing within-group clustering is, unsurprisingly, effectively non-identifiable. Sensitivity analysis can be conducted by investigating the consequences of assuming different values of this parameter. We also demonstrate theoretically and empirically that the estimated probability of a consignment containing contamination and evading detection is almost perfectly robust to mis-specification of the clustering parameter. We apply the new models to large cucurbit seed lots imported into Australia where they provide important new insights on the level of undetected contamination. Supplementary materials accompanying this paper appear on-line.
Publisher: Oxford University Press (OUP)
Date: 17-09-2008
DOI: 10.1111/J.1467-9876.2008.00629.X
Abstract: Studies which measure animals’ positions over time are a vital tool in understanding the process of resource selection by animals. By comparing a s le of locations that are used by animals with a s le of available points, the types of locations that are preferred by animals can be analysed by using logistic regression. Random-effects logistic regression has been proposed to deal with the repeated measurements that are observed for each animal, but we find that this is not feasible in studies where the s le of available points cannot readily be matched to specific animals. Instead, we investigate the use of marginal logistic models with robust variance estimators, by using a study of Australian bush rats as a case-study. Simulation is used to check the properties of the approach and to explore alternative designs.
Publisher: Elsevier BV
Date: 04-2023
Publisher: Elsevier BV
Date: 12-2019
Start Date: 07-2007
End Date: 12-2011
Amount: $75,354.00
Funder: Australian Research Council
View Funded ActivityStart Date: 07-2008
End Date: 06-2011
Amount: $141,211.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2023
End Date: 12-2025
Amount: $552,033.00
Funder: Australian Research Council
View Funded Activity