psi: Create Discrimination Probabilities (Psi) from Data Frame
Description
Creates matrices with discrimination probabilities, number of trials, number
of different answers, and stimulus intensities from a data frame.
Usage
psi(data, oa1 = "s1", oa2 = "s2", resp = "resp")
Arguments
data
data frame with repeated same-different judgments.
oa1, oa2
name of the variable that contains the stimulus intensities
in the first and second observation area.
resp
name of response variable for same-different judgments;
answers have to be d and s for "different" and "same"
response, respectively.
Value
An object of class psi that consists of the following components:
prob
a matrix of discrimination probabilities per stimulus
combination.
ntrials
a matrix of number of trials per stimulus combination.
freq
a matrix of frequencies of different answers per stimulus
combination.
x, y
(if possible numeric) vectors of stimulus intensities.
Details
The data frame must include at least a column for the response and one
column each for observation areas one and two. The return value of
psi may serve as an input to qdm that fits a
quadrilateral dissimilarity model to the judgments.