Dear R forum, I have a concern regarding a mathematical expression of the probability function (see below). I know how to write it for only one index i, but we have two : i (country) and j (year). We have a set of N observations of country year ij (or ith country in jth year). Basically, I could replace ij as a one index t and call it as a country year observation. Anyway, how to write this expression correctly for two indices i and j? Or shall we put two product signs instead? The expression is similar to this: Large Mathematical Sign of Product as a function of (Xij), where the low subscript of the Product is ij=1 and an upper subscript is ij=N. Thanks, Julia _________________________________________________________________ Search that pays you back! Introducing Live Search cashback. rchpaysyouback [[alternative HTML version deleted]]