Journal ArticleDOI
Formulating mixed models for experiments, including longitudinal experiments
TLDR
This article describes a method for deriving the terms in a mixed model and describes the mixed model analysis of data from a three-phase experiment to investigate the effect of time of refinement on Eucalyptus pulp from four different sources.Abstract:
Mixed models have become important in analyzing the results of experiments, particularly those that require more complicated models (e.g., those that involve longitudinal data). This article describes a method for deriving the terms in a mixed model. Our approach extends an earlier method by Brien and Bailey to explicitly identify terms for which autocorrelation and smooth trend arising from longitudinal observations need to be incorporated in the model. At the same time we retain the principle that the model used should include, at least, all the terms that are justified by the randomization. This is done by dividing the factors into sets, called tiers, based on the randomization and determining the crossing and nesting relationships between factors. The method is applied to formulate mixed models for a wide range of examples. We also describe the mixed model analysis of data from a three-phase experiment to investigate the effect of time of refinement on Eucalyptus pulp from four different sources. Cubic smoothing splines are used to describe differences in the trend over time and unstructured covariance matrices between times are found to be necessary.read more
Citations
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Journal ArticleDOI
On the Analysis of Combined Experiments
TL;DR: The rationale for decisions about the inclusion or exclusion of fixed by random effects in a mixed model is presented and it is found that where the effects of treatments over broad populations of environments are to be estimated, it is often most appropriate to include only those fixed byrandom effects that reference experimental units.
Journal ArticleDOI
Accounting for variation in designing greenhouse experiments with special reference to greenhouses containing plants on conveyor systems
TL;DR: An investigation of alternative experimental designs for equally-replicated experiments revealed that generally designs with smaller blocks performed best, but that (nearly) trend-free designs can be effective when blocks are larger.
Journal ArticleDOI
Long-Term Experiments with cropping systems: Case studies on data analysis
TL;DR: In this article, an example-based approach, built upon a number of datasets, covering the main types of LTEs, with increasing levels of complexity, is outlined to build statistical models for data analysis that is useful for all LTEs characterised by the simultaneous presence of all rotation phases in all years, together with within-year replication.
Journal ArticleDOI
Multiple Factors Affect Socioeconomics and Wellbeing of Artisanal Sea Cucumber Fishers.
Steven W Purcell,Poasi Ngaluafe,Simon Foale,Nicole A Cocks,Brian R. Cullis,Watisoni Lalavanua,Watisoni Lalavanua +6 more
TL;DR: Strong evidence for co-dependence among small-scale fisheries, through fall-back livelihood preferences of fishers, suggests that resource managers must mitigate concomitant effects on other fisheries when considering fishery closures.
Journal ArticleDOI
Analysis of series of variety trials with perennial crops
Hans-Peter Piepho,T. Eckl +1 more
TL;DR: In this paper, the use of mixed models for the analysis of field trials with perennial crops has been discussed, and the results of two-stage analysis are shown to be very similar to those of single stage analysis, if serial correlation is properly taken into account.
References
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Book
Mixed-Effects Models in S and S-PLUS
TL;DR: Linear Mixed-Effects and Nonlinear Mixed-effects (NLME) models have been studied in the literature as mentioned in this paper, where the structure of grouped data has been used for fitting LME models.
Journal ArticleDOI
Random-effects models for longitudinal data
Nan M. Laird,James H. Ware +1 more
TL;DR: In this article, a unified approach to fitting two-stage random-effects models, based on a combination of empirical Bayes and maximum likelihood estimation of model parameters and using the EM algorithm, is discussed.
Journal ArticleDOI
Pseudoreplication and the Design of Ecological Field Experiments
TL;DR: Suggestions are offered to statisticians and editors of ecological journals as to how ecologists' under- standing of experimental design and statistics might be improved.
Book
Linear Mixed Models for Longitudinal Data
Geert Verbeke,Geert Molenberghs +1 more
TL;DR: Using data of 955 men, Brant et al showed that the average rates of increase of systolic blood pressure (SBP) are smallest in the younger age groups, and greatest in the older agegroups, and that obese individuals tend to have a higher SBP than non-obese individuals.