(Häfner 2004, Definition 3.12, p. 42) Häfner, Reinhold (2004). Stochastic Implied Votality: A Factor-Based Model. Lecture Notes in Economics and Mathematical Systems (Paperback ed.). Berlin: Springer-Verlag. ISBN978-3-540-22183-8.
(Häfner 2004, Section 5.3.1, Choice of Moneyness Measure, pp. 85–87) Häfner, Reinhold (2004). Stochastic Implied Votality: A Factor-Based Model. Lecture Notes in Economics and Mathematical Systems (Paperback ed.). Berlin: Springer-Verlag. ISBN978-3-540-22183-8.