gm.screening {gmvalid}R Documentation

Model Screening

Description

Preliminary model search procedure for categorical data in three steps, using Goodman's and Kruskal's gamma and chi-squared tests.

Usage

gm.screening(data, conf.level = 0.95)

Arguments

data Data frame or array. Variables need to be discrete and should have names.
conf.level Confidence level (default is 0.95).

Details

The initial model screening divides into three parts: (1) An edge is added to the main effects model, if the marginal gamma coefficient or the chi-squared statistic is significant. (2) An edge is added between two vertices, if either the conditional gamma coefficient or the conditional chi-squared statistic is significant for the two variables given any possible variable in condition. (3) All triplets of variables whose vertices build a complete subgraph are tested for removal using the conditional gamma coefficient and conditional chi-squared statistic. An edge is removed if the corresponding p-value is larger than 1 - conf.level.

Value

mat Adjacency matrix of the screened model.
model String of the graphical model.

Note

The model screening is not a model selection strategy! It 'just' searches for a good start model to initialize a model selection. Common usage is to select a model after screening based on a backwards and forwards selection as implemented in gm.coco.

Author(s)

Ronja Foraita, Fabian Sobotka
Bremen Institute for Prevention Research and Social Medicine
(BIPS) http://www.bips.uni-bremen.de

References

Kreiner S and Edwards D (1983) The analysis of contingency tables by graphical models Biometrika, 70(3):553-565

Kreiner S (2008) DIGRAM http://staff.pubhealth.ku.dk/~skm/skm/ last accessed 30.06.2008

Siersma V (2007) Studies in the interactions between disease development and interventions PhD thesis, Faculty of Health Sciences, University of Copenhagen.

See Also

backward, gm.coco, gm.chi, gm.gamma

Examples

  data(wam)
  model <- gm.screening(wam)
  gm.coco(wam,recursive=TRUE,criterion="aic",model=model$model)

[Package gmvalid version 1.2 Index]