Forms a model-definition structure for a `REML`

analysis (R.W. Payne).

### Options

`MODELSTRUCTURE` = pointer |
Specifies the model-definition structure; no default (must be specified) |
---|---|

`DESCRIPTION` = text |
Description of the model (for output) |

`FIXED` = formula |
Fixed model terms; default `*` |

`CONSTANT` = string token |
How to treat the constant term (`estimate` , `omit` ); default `esti` |

`FACTORIAL` = scalar |
Limit on the number of factors or covariates in each fixed term; default 3 |

`CADJUST` = string token |
What adjustment to make to covariates before analysis (`mean` , `none` ); default `mean` |

`CHANGEITEMS` = string tokens |
What changes to make to an existing model-definition structure (`description` , `fixed` , `constant` , `factorial` , `cadjust` , `random` , `initial` , `constraints` ); if this is unset, the structure is redefined completely |

`IMODELSTRUCTURE` = pointer |
Specifies the initial model-definition structure, to modify when `CHANGEITEMS` is set; default is to modify the one specified by `MODELSTRUCTURE` |

`EXPERIMENTS` = factor |
Factor defining the different experiments in a multi-experiment (meta-) analysis |

### Parameters

`RANDOM` = formula |
Random model terms |
---|---|

`INITIAL` = scalars |
Initial values for each component |

`CONSTRAINTS` = string tokens |
How to constrain each variance component and the residual variance (`none, positive, fixrelative, fixabsolute` ); must be set unless `MODIFY=yes` |

### Description

`VFMODEL`

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`

and `VFSTRUCTURE`

procedures (these define the model settings controlled by the `VCOMPONENTS`

and `VSTRUCTURE`

directives, respectively). The model-definition structures can then 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 model-definition structure is specified by the `MODELSTRUCTURE`

option, which must be set. The `DESCRIPTION`

option supplies a (brief, one-line) description to identify the model in the output.

Details of the model are specified by the `FIXED`

, `CONSTANT`

, `FACTORIAL`

, `CADJUST`

and `EXPERIMENTS`

options, and the `RANDOM`

, `INITIAL`

, `CONSTRAINTS`

parameters (which correspond to those options and parameters of the `VCOMPONENTS`

directive).

You can set the `CHANGEITEMS`

option to modify an existing model-definition structure, instead of redefining it. Its settings then specify which aspects are to be changed. By default, the existing definition structure is supplied by `MODELSTRUCTURE`

(and the modified structure replaces the existing one). Alternatively, if you want to keep the existing structure, you can specify it separately, using the `IMODELSTRUCTURE`

option.

Options: `MODELSTRUCTURE`

, `DESCRIPTION`

, `FIXED`

, `CONSTANT`

, `FACTORIAL`

, `CADJUST`

, `CHANGEITEMS`

, `IMODELSTRUCTURE`

, `EXPERIMENTS`

.

Parameters: `RANDOM`

, `INITIAL`

, `CONSTRAINTS`

.

### See also

Directives: `REML`

, `VCOMPONENTS`

, `VSTRUCTURE`

.

Procedures: `VARANDOM`

, `VFSTRUCTURE`

, `VMODEL`

.

Commands for: REML analysis of linear mixed models.

### Example

CAPTION 'VFMODEL example',\ 'Slate Hall Farm data (Guide to REML in Genstat, Section 1.8).';\ STYLE=meta,plain SPLOAD '%gendir%/data/slatehall.gsh' " define model for analysis as a Lattice square design " VFMODEL [MODELSTRUCTURE=Latticesq; DESCRIPTION='Lattice square analysis';\ FIXED=variety] replicates/(rows*columns) VMODEL Latticesq REML yield