The Generalisability of an Individual's Progress

Instruction cannot be really personalised, as long as assessment remains norm‐referenced. Whereas psychometrics aims at differentiating the performances of individuals at a given moment, edumetrics aims at differentiating stages of learning for a given individual. The structure of the two projects is the same and generalisability theory offers symmetrical formulae for estimating the reliability of each of these measurement designs. An example is presented in this paper which shows that satisfactory reliability can be obtained in an edumetric situation, where the between‐pupils variance is completely ignored. Even though the absolute error variance is the same in both cases, the relative error variances and hence the standard errors of measurement are different. As the true score variances are also different, the edumetric properties of a test should be considered alongside its psychometric ones. Certification of progress by the teacher, supporting a portfolio of achievement, could even have a summative, as well as a formative, function.