calcEAP: Calculate EAP Scores

In akaat/MTBfx: Functions to support Mobile Toolbox analysis

Calculate EAP Scores

Description

This function updates the current probability grid and calculates its mean and standard deviation, which results in the expected a posteriori (EAP) score and one index of the reliability of that score. An alternative reliability indicator would be the standard error calculated from the information matrix but that is not calculated herein. The Mobile Toolbox standard is the SD of the probability grid.

Usage

calcEAP(currentProbGrid, item, i_resp, probDiff, thetaGrid)

Arguments

currentProbGrid	The probability grid must be supplied to weight the item information matrix. It may be the normal density (e.g., if no items have been calculated), or it may be the density of the current EAP score estimate.
item	An index for the item which was just administered.
i_resp	The chosen response category, indexed from 1.
probDiff	The difference between category response probabilities, which is returned by the matrixInfoGRM function.
thetaGrid	A vector of theta estimates at which the test information will be calculated. The thetaGrid is not provided by default, insofar as it expected to be passed by the GRM engine to the function. But if this function is intended to be used alone, a reasonable thetaGrid would be a sequence from -4 to +4 incremented by 0.01 (which is the PROMIS defaults).

Details

Note that this function is normally called within the GRM engine and thus not utilized on its own. It updates the EAP score for one new item. To use this function alone or to conduct pattern-based scoring, one would need to loop over all of the items outside of the function.

Value

This function returns three values. The first is the probability grid, updated after administering/scoring this item. This is a vector the same length as the previous pobability grid (and should be the same length as the thetaGrid). The second element is the estimated theta score using the EAP scoring method. The final element is the standard deviation of the probability grid, which provides an index for the reliability of the score estimate.

See Also

Other GRM_CAT functions: grmCAT(), matrixInfoGRM(), selectMPWI()

Examples

#
sdEAP <- 3
thetaGrid <- seq(-4, 4, length.out=121)
muEAP <- 0
currentProbGrid <- 1/(sdEAP * sqrt(2*pi))*exp((-(thetaGrid - muEAP)^2)/(2*sdEAP^2))

# not run
# calcEAP(currentProbGrid = currentProbGrid, i_resp = 1, probDiff = , thetaGrid = thetaGrid)

akaat/MTBfx documentation built on June 6, 2023, 11:43 p.m.