item_difficulty: Difficulty of Questionnaire Items
Description
Compute various measures of internal consistencies
for tests or item-scales of questionnaires.
Usage
item_difficulty(x)
Value
A data frame with three columns: The name(s) of the item(s), the item
difficulties for each item, and the ideal item difficulty.
Arguments
x
Depending on the function, x may be a matrix as
returned by the cor()-function, or a data frame
with items (e.g. from a test or questionnaire).
Details
This function calculates the item difficulty, which should
range between 0.2 and 0.8. Lower values are a signal for
more difficult items, while higher values close to one
are a sign for easier items. The ideal value for item difficulty
is p + (1 - p) / 2, where p = 1 / max(x). In most
cases, the ideal item difficulty lies between 0.5 and 0.8.