Adds a two-dimensional spline model to a model-definition structure for a REML analysis (R.W. Payne).
Options
IMODELSTRUCTURE = pointer |
Specifies the initial model-definition structure; default is to modify the one specified by MODELSTRUCTURE |
REPLICATES = factor |
Replicate factor, if relevant |
ROWS = factor |
Row factor |
COLUMNS = factor |
Column factor |
Parameters
SPECIFICATION = pointers |
Information required to form the spline model |
MODELSTRUCTURE = pointers |
Model-definition structure, updated to contain the spline model; no default (must be specified) |
DESCRIPTION = texts |
Description of the model (for output); if this is not set, the existing description (from IMODELSTRUCTURE or MODELSTRUCTURE) is retained |
Description
VFSPLINE is one of a suite of procedures designed to simplify the assessment of alternative models for a REML analysis. The first step is to form a model-definition structure for each candidate model, using the VFMODEL procedure. (This defines the model settings controlled by the VCOMPONENTS directive). You can then use the VFSTRUCTURE procedure to define correlation models on the random terms. An alternative is to use this procedure to update the model-definition structure to include a 2-dimensional spline model. (It is possible to include both correlation and spline models, but usually these would be alternatives.)
Model-definition structures can be used as input to procedures like VARANDOM, which assesses possible random models. VARANDOM uses VMODEL to specify each model, in turn, so that it can fit it using REML. The relevant results from each fit are saved by the VRACCUMULATE procedure, so that a decision about the recommended random model can be made once they have all been tried.
The information required to form the terms for the spline model is supplied, in a pointer, by the SPECIFICATION parameter. This can be formed by the FVASPLINESPECIFICATION procedure. You must also set the ROWS and COLUMNS options to the row and column factors for the design. Some spline models also need a replicate factor. You can also supply this with the REPLICATES option. Inside VFSPLINE, the factors and the spline information are used by the VASPLINE procedure to form the spline terms.
The updated model-definition structure (including the spline terms) is saved by the MODELDEFINITION parameter. You can use the IMODELDEFINITION option to specify the original model-definition structure. If IMODELDEFINITION is not set, the MODELDEFINITION must already have been defined (and this is then updated).
The DESCRIPTION option can supply a (brief, one-line) description to identify the model in the output. If this is not set, the description of the original model-definition structure is retained.
Options: MODELSTRUCTURE, DESCRIPTION, FIXED, CONSTANT, FACTORIAL, CADJUST, CHANGEITEMS, IMODELSTRUCTURE, EXPERIMENTS.
Parameters: RANDOM, INITIAL, CONSTRAINTS.
See Also
Directives: REML, VCOMPONENTS, VSTRUCTURE.
Procedures: FVASPLINESPECIFICATION, VASPLINE, VARANDOM, VFSTRUCTURE, VMODEL.
Commands for: REML analysis of linear mixed models.
Example
CAPTION 'VFSPLINE example','Wheat trial in 22 x 15 grid';\
STYLE=major,plain
SPLOAD [PRINT=summary] '%Data%/Wheat22x15.gsh'
" base specification "
VFMODEL [MODELSTRUCTURE=W22x15; DESCRIPTION='Wheat trial in 22 x 15 grid';\
FIXED=Rep+RowGrp+ColGrp] Genotype
" add p-spline degree 3, order of difference 2 "
FVASPLINE vaspec; LINEARPLANE=include
VFSPLINE [IMODELSTRUCTURE=W22x15; REPLICATES=Rep; ROWS=Row; COLUMNS=Column]\
vaspec; MODELSTRUCTURE=W22x15spline; DESCRIPTION='pspline'
VMODEL W22x15spline
REML [MAXCYCLE=100] Yield