2015-03 Uncertainty Evaluation of Computer Simulation Models (Draft Report)

Deterministic agricultural and agro-ecosystem systems models have an important role worldwide. Although these models are mathematically deterministic, there are many possible sources of uncertainty that can propagate through the model. The development of tools to evaluate uncertainty in deterministic models is an active area of research. There are a number of options for model uncertainty evaluation that have been discussed in the literature. The objectives of this review paper are threefold: 1. To describe a formalised state-space framework within which to describe the types and sources of uncertainty that arise in computer simulation models. 2. To provide a framework to carry out a robust uncertainty evaluation of a computer simulation model. 3. To summarise a selection of relevant sampling and analysis techniques for the uncertainty evaluation of computer simulation models.

Esther Meenken, Chris Triggs et al.

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2013-10 Automatic Conversion of Tables to LongForm Dataframes

TableToLongForm automatically converts hierarchical Tables
intended for a human reader into a simple LongForm Dataframe that is
machine readable, hence enabling much greater utilisation of the data.
It does this by recognising positional cues present in the hierarchical
Table (which would normally be interpreted visually by the human brain)
to decompose, then reconstruct the data into a LongForm Dataframe. The
article motivates the benefit of such a conversion with an example
Table, followed by a short user manual, which includes a comparison
between the simple one argument call to TableToLongForm, with code for
an equivalent manual conversion. The article then explores the types of
Tables the package can convert by providing a gallery of all recognised
patterns. It finishes with a discussion of available diagnostic methods
and future work.

Jimmy Oh

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2013-8 Selection and Navigation of Overlapping SVG Objects

SVG is a vector graphic image format that can be used with
browsers to deploy dynamic, interactive graphics over the web. We
present a method that enables generalised Selection and Navigation of
Overlapping SVG Objects by toggling pointer-events CSS styles and the
use of the mousewheel, adding another tool developers can use to grant
users greater and more intuitive interaction with SVG images. We also
present several live examples that demonstrate the method in practice,
both on script generated SVG images and an externally generated SVG image

Jimmy Oh

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2013-7 Advanced SVG Graphics from R

The gridSVG package has recently provided an interface for
some more advanced SVG graphics features: gradient fills and pattern
fills, clipping paths, masks, and filters. This report describes a
simple test case for some of these advanced graphics features and then
explores some ideas for making use of these features in Statistical
Graphics.

Paul Murrell and Simon Potter

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2013-6 Testing for Carryover Effects After Cessation of Treatments: A Parallel Design Approach Does Not Work

In interventions it may be important to determine whether the benefits extend beyond the active treatment period. This is clearly of interest for intensive lifestyle interventions, and there are also examples in the pharmaceutical literature. We consider estimation of carryover effects on time-to-event outcomes such as incident hypertension or incident diabetes. These are defined by a noisy measurement exceeding a diagnostic threshold, and diagnosis is followed by interventions that make subsequent measurements useless for treatment comparison.

We present the results of a systematic simulation study to determine the ability of a parallel-group trial design to detect carryover. None of the designs we examined had acceptable Type I error rate; most also had low power. When a treatment is effective during the intervention period, reliable testing for a carryover effect is difficult. Parallel-group designs do not appear to be a feasible approach.

Sarah Gwynn Sturdevant and Thomas Lumley

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