Investigating Mokken scalability of dichotomous items by means of ordinal latent class analysis

A method for investigating whether a set of items satisfies the conditions of a ‘latent scale’ is proposed. It is based on an adaptation of the latent class model in which the requirement of ‘double monotony’ is translated into systems of inequalities on the item response probabilities. The problem of obtaining the maximum likelihood estimates of the model parameters is discussed. Finally, this method is applied to real data from a large survey.