8.5 Item-level Relative Fit measures (Cont’d)

If this item is a DINA item, we have $$P(10)=P(01)=P(11)$$ This is equivalent to say $$\begin{bmatrix} 0 & 1 & -1 & 0\\ 0 & 0 & 1 & -1\\ \end{bmatrix} \begin{bmatrix} P(00)\\ P(10)\\ P(01)\\ P(11)\\ \end{bmatrix}=\begin{bmatrix} 0\\ 0\\ \end{bmatrix}$$ Or, $$\mathbf{R}\mathbf{P}=\mathbf{0}$$