catR (version 2.2)

startItems: Selection of the first items

Description

This command selects the first items of the adaptive test, either randomly or on the basis of their difficulty level.

Usage

startItems(itemBank, fixItems=NULL, seed=NULL, nrItems=1,
 	 theta=0, halfRange=2, startSelect="bOpt")

Arguments

itemBank

an item bank of class itBank as output of the function createItemBank.

fixItems

either a vector of integer values or NULL (default). See Details.

seed

either a numeric value or NULL (default).Ignored if fixItems is not NULL. See Details.

nrItems

numeric: the number of starting items to be selected (default is 1). Ignored if fixItems is not NULL.

theta

numeric: the initial ability level for selecting the first items (default is 0). Ignored if either fixItems or seed is not NULL. See Details.

halfRange

numeric: the half of the range of initial ability values (default is 2). Ignored if either fixItems or seed is not NULL. See Details.

startSelect

character: the criterion for selecting the first items. Possible values are "bOpt" (default) and "MFI". See Details.

Value

• A list with four arguments:
• items
  the selected items (identified by their number in the item bank).
• par
  the matrix of item parameters of the selected items (one row per item).
• thStart
  the sequence of starting ability values used for selecting the items.
• startSelect
  the value of the startSelect argument.

code

halfRange

itemize

• the set (-1, 1) can be obtained by specifying the triplet to (2, 0, 1);

item

• the set (-1, 0, 1) can be obtained by specifying the triplet to (3, 0, 1);
• the set (-1, 0, 1, 2) can be obtained by specifying the triplet to (4, 0.5, 1.5);
• etc.

Details

This function permits to select the first items of the test. The number of starting items is given by the nrItems argument, with default value 1. The first item(s) of the adaptive test can be selected by one of the following methods.

1. By specifying the item(s) to be administered. The argumentfixItemsthen holds the item number(s) as listed in the item bank. SettingfixItemstoNULL(default value) disables this method.

By selecting it (them) randomly into the item bank. The argument seed permits to fix the random selection by specifying the random seed number. Setting seed to NULL (default value) disables this method. By selecting the item(s) according to an initial sequence of ability values (see below). In this case, two criteria can be used: either one selects the item(s) whose difficulty level is as close as possible to the inital ability value(s), or one selects the most informative item(s) for the given initial ability value(s). The criterion is specified by the startSelect argument, with values "bOpt" (default) for the 'difficulty' criterion, and "MFI" for the 'information' criterion.

References

Magis, D., and Raiche, G. (in press). Random generation of response patterns under computerized adaptive testing with the R package catR. Journal of Statistical Software.

See Also

createItemBank, testList

Examples

# Loading the 'tcals' parameters 
 data(tcals)

 # Item bank creation with 'tcals' item parameters
 bank <- createItemBank(tcals)
 
 # Random selection of 4 starting items
 startItems(bank, seed=1, nrItems=4)

 # Selection of the first 5 starting items
 startItems(bank, fixItems=1:5)

 # Selecting 1 starting item, initial ability estimate is 0
 startItems(bank) 

 # Selecting 3 starting items, initial ability estimate is 1
 # and half range is 2
 startItems(bank, nrItems=3, theta=1, halfRange=2) 

 # Idem but with 'information' criterion
 startItems(bank, nrItems=3, theta=1, halfRange=2, startSelect="MFI")
 
 # Selecting 5 starting items, initial ability estimate is 2
 # and half range is 3
 startItems(bank, nrItems=5, theta=2, halfRange=3)