Waldtest {eRm} R Documentation

## Item-Specific Wald Test

### Description

Performs a Wald test on item-level by splitting subjects into subgroups.

### Usage

## S3 method for class 'Rm'
Waldtest(object, splitcr = "median")
## S3 method for class 'wald'
print(x,...)


### Arguments

 object Object of class RM. splitcr Split criterion for subject raw score splitting. median uses the median as split criterion, mean performs a mean-split. Optionally splitcr can also be a dichotomous vector which assigns each person to a certain subgroup (e.g., following an external criterion). This vector can be numeric, character or a factor. x Object of class wald. ... Further arguments passed to or from other methods. They are ignored in this function.

### Details

Items are eliminated if they not have the same number of categories in each subgroup. To avoid this problem, for RSM and PCM it is considered to use a random or another user-defined split. If the data set contains missing values and mean or median is specified as splitcriterion, means or medians are calculated for each missing value subgroup and consequently used for raw score splitting.

### Value

Returns an object of class wald containing:

 coef.table Data frame with test statistics, z- and p-values. betapar1 Beta parameters for first subgroup se.beta1 Standard errors for first subgroup betapar2 Beta parameters for second subgroup se.beta2 Standard errors for second subgroup se.beta2 Standard errors for second subgroup spl.gr Names and levels for splitcr. call The matched call.

### Author(s)

Patrick Mair, Reinhold Hatzinger

### References

Fischer, G. H., and Molenaar, I. (1995). Rasch Models - Foundations, Recent Developements, and Applications. Springer.

Fischer, G. H., and Scheiblechner, H. (1970). Algorithmen und Programme fuer das probabilistische Testmodell von Rasch [Algorithms and programs for Rasch's probabilistic test model]. Psychologische Beitraege, 12, 23-51.

LRtest, MLoef
#Wald test for Rasch model with user-defined subject split