Let us use the notation of Rating Scale Analysis (Wright & Masters, 1982)
p. 100
Xni = the observation generated by person n on item i
Eni = its expectation = sum k*Pnik, for k = 0,m
Yni = its residual = Xni - Eni
Wni = its variance = sum (k*k*Pnik) - Eni*Eni, for k = 0,m
Then the logit bias for subset S of persons on item i is
Bias(S) = sum (Yni) / sum (Wni) where sum is across all n in S
Standard error of Bias is
SE (S) = sqrt ( sum (Wni) ) where sum is across all n in S
Statistical significance of Logit Bias departure from its expectation of 0.0 is
t = Bias(S)/SE(S)
MESA Research Note #1 by John Michael Linacre, April 1997
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