This study develops a model which converts stated buying intentions into purchase probabilities. It derives upper and lower bounds on subsequent proportions of buyers from intention data and shows the consistency of those bounds with actual proportions of buyers for several data sets. Link to the article
BEMMAOR, A.C. (1995). Predicting Behavior from Intention-to-buy Measures: The Parametric Case. Journal of Marketing Research, 32(2), pp. 176-191.