Exploring equivalent forms reliability using a key stage 2 reading test

Abstract

This article outlines an empirical investigation into equivalent forms reliability using a case study of a national curriculum reading test. Within the situation being studied, there has been a genuine attempt to create several equivalent forms and so it is of interest to compare the actual behaviour of the relationship between these forms to the relationship that would be expected theoretically. As such, this article not only reports the estimated levels of reliability based on several equivalent forms but also compares these to the levels of that would be expected from internal reliability estimates. Reliability is quantified both in terms of correlations and in terms of decision consistency. Results of analysis show a relatively good agreement between internal and equivalent forms estimates of reliability. The small discrepancies that exist tend to involve the internal estimates of reliability being higher than the equivalent forms estimates. Differences between the estimates are likely to be caused by sources of measurement error that are not captured in internal estimates. Within the situation under investigation, this may include marking and occasion-related errors.