| convP2PN {lazy.irtx} | R Documentation |
Convert Partial Credit Item Parameters in Standard Format to Partial Credit Item Parameters in Nominal Format
convP2PN(param, print = 0, DinP = 1, ctype = 0)
param |
Item Parameter Data Frame |
print |
= 1 to print result |
DinP |
= 1 to include D=1.7 in logistic function |
ctype |
= 1 to convert to type PN with c-parameters |
ICRF of category k of item j at theta, namely, p_{jk}(theta)
is defined as
p_{jk}(theta) = Ez_{jk}(theta)
/ sum_{k=0}^{ncat[j]-1} Ez_{jk}(theta)
where
if type = "PN" and ctype=0,
Ez_{jk}(theta) = exp( 1.7^DinP a_j k (theta - b_{jk}) )
, k=0,1, ..., ncat[j]-1
with b_{j0}=0.
if type = "PN" and ctype=1,
Ez_{jk}(theta) = exp( a_j k theta + c_{jk}) )
, k=0,1, ..., ncat[j]-1
with c_{j0}=0.
Note that if DinP=1, 1.7 will be used.
This b*_{jk} is the original step parameter and it is
the value of theta where P_{jk-1} and P_{jk} intersect.
Partial Credit Item Parameter Data Frame in Nominal Format
temp <- irf( paramS1[4,], plot=1 ) temp <- irf( convP2PN(paramS1[4,]), plot=1 ) temp1 <- convP2PN(paramS1[4,]) temp2 <- convPN2P(temp1) Print(paramS1[4,],temp1,temp2) temp1 <- convP2PN(paramS1[4,], ctype=1) temp2 <- convPN2P(temp1, ctype=1) Print(paramS1[4,],temp1,temp2)