Overview (GENLOG command)

GENLOG is a general procedure for model fitting, hypothesis testing, and parameter estimation for any model that has categorical variables as its major components. As such, GENLOG subsumes a variety of related techniques, including general models of multiway contingency tables, logit models, logistic regression on categorical variables, and quasi-independence models.

GENLOG, following the regression approach, uses dummy coding to construct a design matrix for estimation and produces maximum likelihood estimates of parameters by means of the Newton-Raphson algorithm. Since the regression approach uses the original parameter spaces, the parameter estimates correspond to the original levels of the categories and are therefore easier to interpret.

HILOGLINEAR, which uses an iterative proportional-fitting algorithm, is more efficient for hierarchical models and useful in model building, but it cannot produce parameter estimates for unsaturated models, does not permit specification of contrasts for parameters, and does not display a correlation matrix of the parameter estimates.

The General Loglinear Analysis and Logit Loglinear Analysis dialog boxes are both associated with the GENLOG command. In previous releases, these dialog boxes were associated with the LOGLINEAR command. The LOGLINEAR command is now available only as a syntax command. The differences are described in the discussion of the LOGLINEAR command.

Options

Cell Weights. You can specify cell weights (such as structural zero indicators) for the model with the CSTRUCTURE subcommand.

Linear Combinations. You can compute linear combinations of observed cell frequencies, expected cell frequencies, and adjusted residuals using the GRESID subcommand.

Generalized Log-Odds Ratios. You can specify contrast variables on the GLOR subcommand and test whether the generalized log-odds ratio equals 0.

Model Assumption. You can specify POISSON or MULTINOMIAL on the MODEL subcommand to request the Poisson loglinear model or the product multinomial loglinear model.

Tuning the Algorithm. You can control the values of algorithm-tuning parameters with the CRITERIA subcommand.

Output Display. You can control the output display with the PRINT subcommand.

Optional Plots. You can request plots of adjusted or deviance residuals against observed and expected counts, or normal plots and detrended normal plots of adjusted or deviance residuals using the PLOT subcommand.

Basic Specification

The basic specification is one or more factor variables that define the tabulation. By default, GENLOG assumes a Poisson distribution and estimates the saturated model. Default output includes the factors or effects, their levels, and any labels; observed and expected frequencies and percentages for each factor and code; and residuals, adjusted residuals, and deviance residuals.

Limitations

  • Maximum 10 factor variables (dependent and independent).
  • Maximum 200 covariates.

Subcommand Order

  • The variable specification must come first.
  • Subcommands can be specified in any order.
  • When multiple subcommands are specified, only the last specification takes effect.