A - Notation

The notation in this chapter follows Wright and Masters (1982).

Section Symbol Term Description
4.6 \(\beta_n\) Ability True (but unknown) developmental score of child \(n\)
4.6 \(\delta_i\) Difficulty True (but unknown) difficulty of item \(i\)
4.6 \(\pi_{ni}\) Probability True (but unknown) probability that child \(n\) passes item \(i\)
6.1 \(\hat\beta_n\) Ability Estimated developmental score (D-score) of child \(n\)
6.1 \(\hat\delta_i\) Difficulty Estimated difficulty of item \(i\)
6.1 \(P_{ni}\) Probability Estimated probability that child \(n\) passes item \(i\)
6.1 \(x_{ni}\) Data Observed response of child \(n\) on item \(i\), 0 or 1
6.1 \(W_{ni}\) Variance Variance of \(x_{ni}\)
6.1 \(z_{ni}\) Residual Standardized residual between \(x_{ni}\) and \(P_{ni}\)
6.1 \(N\) Count Number of measurements (children)
6.1 \(L\) Count Number of items (milestones)
6.4 \(P(\hat\delta_i)\) Probability Conditional probability of passing item \(i\)
6.4 \(I(\hat\delta_i)\) Information Item information function of item \(i\)
6.5 \(R\) Reliability True test reliability
6.5 \(\hat R\) Reliability Estimated test reliability
6.5 \(\sigma_e^2\) Variance True error variance
6.5 \(\hat\sigma_{\hat e}^2\) Variance Estimated error variance
6.5 \(\hat\sigma_{\hat e}\) Variance Standard error of measurement (sem)
9.2 \(f\) Factor Age-adjustment factor