utilities {elisr}

Miscellaneous utility functions

Description

A set of utility functions to calculate characteristic values of classical test theory, reverse a variable, and extract the relevant bits from various objects.

calc_rit() calculates the corrected item-total correlation of a scale or fragment using a part-whole correction. Thus, the item itself is excluded in the calculation process.

calc_rbar() calculates the average correlation of a fragment or scale.

calc_alpha() calculates the internal consistency of a scale or fragment using Cronbach's alpha.

rvrs_var() reverses an item using the specified scaling values. It handles the following types of scales:

• ...-3 -2 -1 0 1 2 3..., e.g., sclvals = c(-3, 3)

• 0 1 2 3 4 5 6..., e.g., sclvals = c(0, 7)

• 1 2 3 4 5 6 7..., e.g., sclcals = c(1, 7)

rvrs_note() gets the full report of reversed variables and reports a unique list of them.

extr_core() is used to extract all pairs of core items from a fragment.

extr_core_nms() is used to extract the names of all pairs of core items from a given fragment.

extreb_itms() builds the counterpart of a fragment from the given item names. Therefore, the counterpart includes all variables that are not part of a fragment but which are mentioned in the specified data set.

nme_msdf() renames the components of a multiple scaled data frame. The naming scheme is scl_n. scl stands for 'scale' and n specifies the number of fragments or scales. For example, the first component is called scl_1.

Usage

calc_rit(scl, use)

calc_rbar(scl, use)

calc_alpha(scl, use)

rvrs_var(var, sclvals)

rvrs_note(msg, applicant)

extr_core(scl)

extr_core_nms(scl)

extreb_itms(df, itm_nms)

nme_msdf(x)

Arguments

scl

a scale within a multiple scaled data frame.

use

an optional string indicating how to deal with missing values, See use in cor for details.

var

a variable or item (often a column from a data frame).

sclvals

the start- and end point of a scale (specify: c(sp,ep)).

msg

a reverse message sent from either disjoint() or overlap().

applicant

the function which wants to leave messages disjoint() or overlap().

df

a data frame object.

itm_nms

the names of an item from a scale.

x

a multiple scaled data frame.

Details

All functions are internal functions.

Value

calc_rit() returns a numeric vector of length one. It is used to examine the coherence between item and overall score.

calc_rbar() returns a numeric vector of length one that reports the inter-item correlation.

calc_alpha() returns a numeric vector of length one which is used to assess the internal consistency of a scale.

rvrs_var() returns the reversed numeric vector using the above reversing scheme.

rvrs_note() is called for its side effects. It leaves a message when an item is reversed.

extr_core() returns a numeric vector of length two, which contains the two items with the highest correlation in a fragment or scale.

extr_core_nms() returns character vector of length two, which contains the names of the two items with the highest correlation in a fragment or scale.

extrev_itms() returns vector of length m minus two, where 'm' specifies the number of variables in a given data set. It contains the items of a scale's counterpart.

nme_msdf() returns a character vector that numbers each element of its input according to the above naming scheme.