Item-Total correlation (ITC) is a Pearson's correlation of an item with the Number-Right Score (NRS) or total score. This function is applicable only to binary response data.
The ITC is a measure of item discrimination, indicating how well an item distinguishes between high and low performing examinees.
ItemTotalCorr(U, na = NULL, Z = NULL, w = NULL, ...)A numeric vector of item-total correlations. Values typically range from -1 to 1, where:
Values near 1: Strong positive discrimination
Values near 0: No discrimination
Negative values: Potential item problems (lower ability students performing better than higher ability students)
U is a data matrix of the type matrix or data.frame.
na argument specifies the numbers or characters to be treated as missing values.
Z is a missing indicator matrix of the type matrix or data.frame
w is item weight vector
Internal parameters for maintaining compatibility with the binary data processing system. Not intended for direct use.
The correlation is calculated between:
Each item's responses (0 or 1)
The total test score (sum of correct responses)
Higher positive correlations indicate items that better discriminate between high and low ability examinees.
# using sample dataset
ItemTotalCorr(J15S500)
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