Research Discussion Paper – 1974 Equation (6)

\begin{array}{l} ST = E (\frac{WE (1 + TP)}{PN (1 - TI)}, \frac{PT}{PN}, Q) \\ \begin{array}{l} E_{1} < 0 & E_{2} > 0 & E_{3} > 0 \end{array} \end{array}