itemUsageConstraint {eatATA}

Create item usage constraints.

Description

Creates constraints related to item usage. That is, the number of times an item is selected is constrained to be either (a) smaller or equal than (operator = "<="), (b) equal to (operator = "="), or (c) greater or equal than (operator = ">=") the chosen value.

Usage

itemUsageConstraint(
  nForms,
  nItems = NULL,
  formValues = rep(1, nForms),
  operator = c("<=", "=", ">="),
  targetValue = 1,
  whichItems = NULL,
  info_text = NULL,
  itemIDs = NULL
)

Arguments

nForms

Number of forms to be created.

nItems

Number of items in the item pool [optional to create itemIDs automatically].

formValues

vector with values or weights for each form. Defaults to 1 for each form.

operator

A character indicating which operator should be used in the constraints, with three possible values: "<=", "=", or ">=". See details for more information.

targetValue

The value to be used in the constraints

whichItems

A vector indicating which items should be constrained. Defaults to all the items.

info_text

a character string of length 1, to be used in the "info"-attribute of the resulting constraint-object.

itemIDs

a character vector of item IDs in correct ordering, or NULL.

Details

When operator = "<=" and value = 1 (the default), each item can be selected maximally once, which corresponds with assuring that there is no item overlap between the forms. When operator = "=" and value = 1, each item is used exactly once, which corresponds to no item-overlap and complete item pool depletion.

If certain items are required in the resulting test form(s), as for example anchor items, whichItems can be used to constrain the usage of these items to be exactly 1. whichItems can either be a numeric vector with item numbers or a character vector with item identifiers corresponding to itemIDs.

Value

An object of class "constraint".

Examples

## create no-item overlap constraints with item pool depletion
##  for 2 test forms with an item pool of 20 items
itemUsageConstraint(2, operator = "=", targetValue = 1,
                    itemIDs = 1:20)

## force certain items to be in the test, others not
usage1 <- itemUsageConstraint(2, operator = "<=", targetValue = 1,
                    itemIDs = paste0("item", 1:20))
usage2 <- itemUsageConstraint(2, operator = "=", targetValue = 1,
                    itemIDs = paste0("item", 1:20),
                    whichItems = c("item5", "item8", "item10"))