A stochastic model for trial outcomes, which can be classified in, but one of three mutually exclusive and exhaustive classes is proposed. Examples of such a trial include: selecting and testing a unit of certain product, in social and political surveys, where the respondent is asked to form an opinion about certain matter, … etc. The three classes represent success, no change (or stability), and failure. The proposed model has two parameters and . The Maximum Likelihood method is used to estimate these parameters and some properties of the proposed model are presented. An extension of the model is derived for the case of independent trials. An application for the production of a certain factory is given