anchorpoint: Function to produce anchorpoint objects

In lucasmanuelkohler/anchorpoint: Anchor Point Selection Based on the Gini Inequality Criterion

Description

Function to conduct the anchor point selection method of Strobl et al. (2021)

Usage

anchorpoint(
  rm1,
  rm2,
  select = c("CLF Criterion", "Gini Index"),
  grid = c("symmetric", "sparse")
)

Arguments

rm1	Fitted Rasch Model object for the first group of test takers
rm2	Fitted Rasch Model object for the second group of test takers
select	a string, specifying the criterion that is evaluated ("CLF Criterion" or "Gini Index", abbreviations are accepted)
grid	a string, specifying the method that is used to generate the grid of possible shifts to be evaluated

Value

an anchorpoint object containing:

• list with results for global optimum (single grid value and criterion value)

• list with all results (all grid values and criterion values)

• string with used criteria

• string with used grid methods

• list with Rasch Model objects for both groups of test takers

References

• Strobl, C., Kopf, J., Kohler, L., von Oertzen, T. & Zeileis, A. (2021). Anchor point selection: An approach for anchoring without anchoritems. Applied Psychological Measurement, to appear.

Examples

# Load the SPISA data set (general knowledge quiz - more information at ?SPISA)
library("psychotree")
data("SPISA")

# Fit the Rasch Models for the two groups females and males
fit <- anchorpoint::raschFit(SPISA, resp.mat.name='spisa', group.name='gender')

# Rasch Model fit for the first and second group
rm1 <- fit$rm1
rm2 <- fit$rm2

# Fit an Anchorpoint object
ap_object <- anchorpoint(rm1,rm2,select = "Gini Index", grid = "sparse")

# inspect the Anchorpoint object
# The print function summarizes the Global Optimum for the selected methods
print(ap_object)

# The summary function summarizes the Global Optimum for the selected methods
# and shows all the other results
summary(ap_object)

# The plot function shows the criterion plot (criterion value vs. shifts).
plot(ap_object)

# To extract the criterion value and shift for a specific position on the plot,
# set location_picker = TRUE and execute the command.
# Then, click on the desired positions and press ESCAPE.
plot(ap_object, location_picker = TRUE)

lucasmanuelkohler/anchorpoint documentation built on April 16, 2021, 6:41 a.m.