A GENERAL INTRODUCTION TO EXPERIMENTAL DESIGN
(Dr. L. Benedetti Cecchi, University of Pisa, Italy)
Class
1. Logical and philosophical frameworks for the analysis
of ecological complexity
- Falsification and the hypothetic-deductive approach
- Strong inference
- Bayesian inference
2. Sampling populations
- Ecological variables
- Frequency distributions
- Parameters and their estimates
- Precision and accuracy of sample estimates
3. Relationships among ecological models, statistical
models and data
- Estimation and hypothesis testing
- Linear statistical models
- Methods of estimation: OLS and ML
- Statistical hypothesis testing: general hints
4. Experimental design
- Basic concepts: replication, randomisation, independence
- Choosing levels for predictor variables: fixed vs.
random factors
- Relationships among predictor variables: hierarchical
and factorial designs
- Extension to multifactorial designs
5. Applications
- Hierarchical designs: solution to spatial and temporal
confounding
- Hierarchical designs: sampling at multiple scales
in space and time
- Factorial designs: understanding interactions among
predictor variables
- Assessing the generality (or lack thereof) of ecological
processes: multifactorial experiments
Lab (computer- based exercises)
A- Sampling populations: influence of variance and sample
size on sample estimates
B- Estimating spatial and temporal variance: the analysis
of pattern using simulated and real data sets
C- Understanding ecological processes: analysis and
interpretation of real ecological experiments
MULTIVARIATE COMMUNITY ANALYSES USING
PRIMER
(Dr. K.R. Clarke, Dr. R.N. Gorley, Plymouth Marine Laboratory,
UK)
Class
1. Measures of resemblance (similarity/dissimilarity/distance)
in multivariate structure for assemblage & environmental
data, including pre-treatment options (standardisation,
transformation, normalisation) and the effects of different
coefficient choices
2. Hierarchical clustering of samples, including different
linkage options (CLUSTER)
3. Ordination (of environmental data) by Principal Components
Analysis (PCA)
4. Ordination (of assemblage data) by non-metric Multi-Dimensional
Scaling (MDS)
5. Multivariate testing for differences between groups
of samples (1- and 2-way crossed and nested ANOSIM),
and comments on power
6. Determining variables which discriminate groups of
samples (1- and 2-way similarity percentages, SIMPER),
both for species and environmental variables
7. Diversity measures (DIVERSE) and comments on sampling
properties and multivariate treatment of multiple indice.
Dominance plots and tests for differences between sets
of curves (DOMSIM), particle-size distributions etc
8. Taxonomic (or phylogenetic) diversity and distinctness
for quantitative data, or simple species lists, as valid
biodiversity measures (DIVERSE) over broad spatial and
temporal scales; comments on sampling properties and
testing structures (TAXDTEST)
9. Linking potential environmental drivers to an observed
assemblage pattern, via bubble plots, the matching of
multivariate structures (the BIO-ENV procedure), and
linkage trees (LINKTREE, a 'classification and regression
tree' approach)
10. Global hypothesis tests I: of no agreement between
two resemblance matrices (RELATE), comparing assemblage
(or environmental) structure with linear (seriation)
or cyclic models in space and time; also of no evidence
for a biota-environment link, allowing for the selection
effects in finding an optimum match (the global BIO-ENV
test)
11. Stepwise form of the BIO-ENV routine (BVSTEP) generalised
to other comparisons, e.g. species subsets determining
overall assemblage pattern, species best delineating
modelled or observed environmental gradients, environmental
variables best acting as 'proxy' for the full set
12. Second-stage analysis (2STAGE) to compare taxonomic
levels and transformation or coefficient choices; also
for a possible testing framework in some repeated measures
designs
13. Widening the scope of assemblage resemblance measures:
improving the signal to noise ratio by variable down-weighting
of species whose individuals arrive in the sample in
clusters (Dispersion weighting); exploiting ideas of
taxonomic distinctness to define new similarity coefficients
appropriate for data with few, or no, species in common
(Taxonomic dissimilarity)
Lab (computer- based exercises)
A- Clustering and ordination (simple hierarchical clustering
and Principal Components Analysis/non-metric Multi-Dimensional
Scaling)
B- Multivariate ANOSIM tests (simple 1- and 2-way layouts)
for determining and quantifying differences between
groups of samples
C- 1- and 2-way SIMPER
D- DIVERSE, dominance plots and testing sets of curves
(DOMSIM)
E- DIVERSE and TAXDTEST
F- Draftsman plots (to assess variable transforms),
PCA, BIO-ENV and LINKTREE
G- ANOSIM for 2-way without replication, RELATE and
the global BIO-ENV test
H- BEST (the combined BIO-ENV/BVSTEP routine) and 'own
data' session
I- Lab session on 2STAGE, and 'own data' session
L- SIMPROF structure tests in CLUSTER, and using 2STAGE
to compare different similarity coefficients (including
dispersion weighted, hierarchy based etc)
ANALYSING MULTI-SPECIES RESPONSES TO
COMPLEX EXPERIMENTAL DESIGNS
(Dr. M. J. Anderson, University of Auckland, New Zealand)
Class
1. Partitioning variation for a linear model based on
any distance measure: permutational multivariate analysis
of variance (PERMANOVA) and permutational multivariate
multiple regression (PERMREG).
- Analysing complex multi-factor models and analyses
using permutational and Monte Carlo approaches; Principal
coordinate analysis (PCO, or metric MDS) as an unconstrained
ordination method for viewing patterns; Generalised
solution for multiple regression based on linear partitioning
of principal coordinates for any linear model; Solution
for MANOVA based on inter-point distances; Interpreting
multivariate interaction terms; Comparison with other
methods, including assumptions; Estimating pseudo multivariate
variance components based on distances.
2. Permutation tests for complex experimental designs
(ANOVA, multiple regression).
- Permutation of residuals under a reduced or a full
model; Restricted permutations and exact versus asymptotically
exact tests; Choosing the correct units to permute by
reference to expected mean squares; What to do when
there aren't enough permutations; Monte Carlo approximation;
Permutational multivariate multiple regression (PERMREG);
Testing for relationships between species data and one
or more predictor variables; Building a linear model,
using sets of predictor variables and covariables and
choosing correct permutation strategies.
3. Canonical analysis of principal coordinates (CAP),
a constrained ordination method.
- Unconstrained versus constrained ordination techniques
- distinctions and potential pitfalls; Generalised discriminant
analysis based on distances; Cross-validation check
on arbitrariness of results; Correlations with species
variables; Comparison with other methods, including
PERMANOVA; Monte Carlo approximation; Generalised canonical
correlation analysis based on distances; Using canonical
axes to place new observations along an environmental
gradient.
4. Permutational test for differences in multivariate
dispersions among groups (PERMDISP).
- Testing for differences in group dispersions versus
tests of location in multivariate space; Distances from
centroids and non-independence; Defining the multivariate
space for the hypothesis of interest; The effects of
dissimilarity measures and transformations on relative
dispersions; Interpretations by reference to PERMANOVA.
5. Putting it all together - a general approach for
the analysis of species assemblages in complex experimental
designs.
- Unconstrained and constrained ordination; Hypothesis-testing
and multivariate models; Finding individual species
related to significant multivariate patterns.
6. Environmental impact assessment and monitoring
- Environmental impact assessment; Building models and
analysing multivariate data from BACI and beyond-BACI
experimental designs using PERMANOVA and PERMREG; Environmental
monitoring; Multivariate control charts based on distances,
with bootstrap confidence bounds.
Lab (computer- based exercises)
A- PCO (metric MDS) and two-way PERMANOVA and PERMDISP.
B- PERMREG and building multivariate linear models.
C- CAP; Generalised discriminant analysis and canonical
correlation analysis based on distances.
D- PERMANOVA for complex designs and multiple comparisons;
A general strategy for analysis.
E- Environmental impact assessment using PERMANOVA and
PERMREG; using the CONTROLCHART program for environmental
monitoring.
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