Measurement precision in test score and item response models

The population-dependent concept of reliability is used in test score models such as classical test theory and the binomial error model, whereas in item response models, the population-independent concept of information is used Reliability and information apply to both test score and item response models. Information is a conditional definition of precision, that is, the precision for a given subject; reliability is an unconditional definition, that is, the precision for a population of subjects. Information and reliability do not distinguish test score and item response models. The main distinction is that the parameters are specific for the test and the subject in test score models, whereas in item response models, the item parameters are separated from the subject parameters.