Defines the residual term for a REML analysis, or the residual term for an experiment within a meta-analysis (combined analysis of several experiments).
Options
EXPERIMENT = scalar |
Level of the EXPERIMENTS factor for which the residual is being defined |
|---|---|
TERM = formula |
Model term to be used as the residual |
FORMATION = string token |
Whether the structure is formed by direct product construction or by definition of the whole matrix (direct, whole); default dire |
VARIANCE = scalar |
Allows an initial estimate to be provided for the residual variance of the experiment |
CONSTRAINT = string token |
Allows the residual variance to be fixed at its initial value (fix, positive) default posi |
COORDINATES = matrix or variates |
Coordinates of the data points to be used in calculating distance-based models |
Parameters
MODELTYPE = string tokens |
Type of covariance model associated with the term(s), or with individual factors in the term(s) if FORMATION=direct (identity, fixed, AR, MA, ARMA, power, boundedlinear, circular, spherical, linearvariance, banded, correlation, antedependence, unstructured, diagonal, uniform, FA, FAequal) default iden |
|---|---|
ORDER = scalar |
Order of model |
HETEROGENEITY = string token |
Heterogeneity for correlation matrices (none, outside); default none |
METRIC = string token |
How to calculate distances when MODEL=power (cityblock, squared, euclidean); default city |
FACTOR = factors |
Factors over which to form direct products |
MATRIX = identifiers |
To define matrix values for the term or the factors when MODEL=fixed |
INVERSE = identifiers |
To define values for matrix inverses (instead of the fixed matrices themselves) when MODEL=fixed |
INITIAL = identifiers |
Initial parameter values for each correlation matrix |
CONSTRAINTS = texts |
Texts containing strings none, fix or positive to define constraints for the parameters in each model |
EQUALITYCONSTRAINTS = variates |
Non-zero values in the variate indicate groups of parameters whose values are to be constrained to be equal |
Description
VRESIDUAL is used to define the residual term for a REML analysis or to define separate residual terms for different experiments within a multi-experiment (or meta-) analysis. The TERM option is used to specify the formula for the residual term. This term need not have been specified previously by the VCOMPONENTS statement.
For a single experiment, VRESIDUAL can be used to impose a covariance structure on the residual term. This could also be done by specifying the covariance structure using VSTRUCTURE, but VRESIDUAL has the advantage that the algorithm then checks that the correct residual term is used.
In a multi-site experiment, VRESIDUAL can be used to specify a different residual model for each separate experiment. The EXPERIMENT option is used to define the experiment(s) for which the model is to be used.
The VARIANCE option is used to give an initial value for the residual variance in the current experiment(s). You can set option CONSTRAINT=fix to fix the residual variance at the initial value rather than estimating it (as a positive value).
The definition of the residual terms then follows mainly as for the definition of correlated error terms through VSTRUCTURE The exception is that power models can be defined only in terms of the coordinates of the data points, not by specifying coordinates for the factor levels. (So the DISTANCES and COORDINATES parameters of VSTRUCTURE are not present in VRESIDUAL.)
For a multi-experiment analysis, the factors and variates for the separate experiments should be concatenated into structures which run over all the experiments. For example, consider an experiment set up at two sites to compare a set of 24 varieties in four replicates. In one site the experiment was laid out as a grid of eight rows by 12 columns, in the other a grid of 16 rows by six columns was used. In these circumstances, a single set of factors (of length 192) can be used to specify the design, using factors to describe variety, rows and columns, plus a factor expt defining the allocation of units to experiments.
VCOMPONENTS [FIXED=Variety; EXPERIMENTS=Expt]
VRESIDUAL [EXPERIMENT=1; TERM=Row.Col] MODEL=AR,AR;\
ORDER=1,1; FACTOR=Row,Col
VRESIDUAL [EXPERIMENT=2; TERM=Row.Col] MODEL=AR,AR;\
ORDER=1,1; FACTOR=Row,Col
Where some factors differ between experiments, these should be defined on the units relevant to the appropriate experiment(s) and missing elsewhere. When an EXPERIMENTS factor has been defined, the default action of the MVINCLUDE option of REML is changed to include units with missing y-values and missing factor levels.
Options: EXPERIMENT, TERM, FORMATION, VARIANCE, CONSTRAINT, COORDINATES
Parameters: MODEL, ORDER, HETEROGENEITY, METRIC, FACTOR, MATRIX, INVERSE, INITIAL, CONSTRAINTS, EQUALITYCONSTRAINTS.
See also
Directives: REML, VCOMPONENTS, VSTRUCTURE, VPEDIGREE, VSTATUS.
Procedures: VAMETA, VRMETAMODEL.
Commands for: REML analysis of linear mixed models.