psychotree (version 0.13-0)

PCModel: Model-Generating Function for Partial Credit Models

Description

PCModel is a wrapper function that creates a "StatModel" object with certain fitting parameters passed on to PCModel.fit for fitting partial credit models.

Usage

PCModel(nullcats = c("keep", "downcode", "ignore"), reltol = 1e-10,
  deriv = c("sum", "diff"), hessian = TRUE, maxit = 100L)

Arguments

nullcats

character, specifying how items with null categories, i.e., categories not used, are treated (see details in PCModel.fit).

deriv

character. If "sum" (the default), the first derivatives of the elementary symmetric functions are calculated with the sum algorithm. Otherwise ("diff") the difference algorithm (faster but numerically unstable) is used.

hessian

logical. Should the Hessian of the final model be computed? If set to FALSE, the vcov method can only return NAs and consequently no standard errors or tests are available in the summary.

reltol, maxit, ...

further arguments passed to optim.

Value

• PCModel returns an S4 object of class "StatModel" that fits partial credit models with the specified arguments.

Details

PCModel is the S4 interface for PCModel.fit so that it can be used in mob. The user does not have to call this directly but can simply use the pctree interface.

See Also

pctree, PCModel.fit