1. A computer-implemented method for forecasting demand for order configurations, comprising: expressing attach rates associated with n options as a set of n positive numbers whose sum is one, an attach rate representing a proportion of a product for which an option is requested; transforming said attach rates as a random vector in n−1 dimensional Euclidean space; modeling a distribution of the transformed attach rates; estimating a location vector of the distribution by computing point forecasts of the transformed attach rates; estimating a dispersion matrix of the distribution, the dispersion matrix describing variability of forecast errors of the transformed attach rates; and transforming said location vector and said dispersion matrix to forecast attach rates.