| irf {lazy.irtx} | R Documentation |
Calculation of Item Response Function
irf(param, theta = NULL, weight = NULL, zero = 1, smallP = 1e-06, thmin = -4, thmax = 4, npoints = 21, DinP = 1, print = 1, debug = 0, plot = 0, colors = "black", plotchar = NULL, linetype = NULL)
param |
Item Parameter Data Frame |
theta |
Discrete theta values |
weight |
Weight data frame |
zero |
= 0 to exclude the zero-th category from output |
smallP |
Minimum value of probability |
thmin |
Minimum value of discrete thata value |
thmax |
Maximum value of discrete thata value |
npoints |
# of discrete points for theta |
DinP |
= 1 to include D=1.7 in logistic function |
print |
= 1 to print result |
debug |
= 1 to print intemediate result |
plot |
= 1 to plot result |
colors |
= color of the lines in plot |
plotchar |
= pch vector to be used in the plot |
linetype |
= lty vector to be used in the plot |
It is assumed that the data frame has the following columns
in the following order.
name, type, ncat, p1, p2, ..., p[ncat+1]
When item_type == "B" or "B2" or "B3", ( ncat == 2 )
p1 is the discrimination parameter
p2 is the difficulty parameter
p3 is the gussing parameter
When item_type == "G",
p1 is the discrimination parameter
p2 is the category threshold parameter b_j1
p3 is the category threshold parameter b_j2
p_ncat is the category threshold parameter b_j,[ncat-1]
When item_type == "P",
p1 is the discrimination parameter
p2 is the step parameter b_j1
p3 is the step parameter b_j2
p_ncat is the step parameter b_j,[ncat-1]
When item_type == "PN,
p1 is the slope parameter
p2 is the intercept parameter b_j1
p3 is the intercept parameter b_j2
p_ncat is the intercept parameter b_j,[ncat-1]
When item_type == "N,
p1 - p_(ncat[j]-1) are the slope parameters
p_ncat[j] - p_2*(ncat[j]-1) are the intercept parameters
Regardless of the item_type, there will be ncat[j]
item paramters for item j, except for the Binary Items
which have the gusseing param as the ncat[j]+1st,
and the Nominal Items which have 2*(ncat[j]-1) item parameters.
list( ICRF, IRF, TRF, fromP, toP )
where
ICRF npoints x sum(ncat)
IRF npoints x nitems weighted by item category weight
TRF npoints x 1 weighted by item category weight
and item weight
fromP, toP location of each item category in ICRF
Needs:
icrfB, icrfG, icrfPN, icrfP, icrfN, checkparam
Cards=" name type ncat p1 p2 p3 p4 Q1 B 2 0.9 0.0,, Q2 B3 2 1.0 0.0 0.2, Q3 G 4 1.0 -2.0 0.0 2.0 Q4 P 4 0.8 -2.0 0.0 2.0 "; param <- cards( Cards, header=1 ) irf( param, plot=1 )