This paper reports on the analysis of a large global sample of live Aptis test data to investigate to what extent the theoretical assumptions hold regarding the central role accorded to the grammar and vocabulary (or Core) component of the test.
The report first addresses the relationship between grammar and vocabulary as operationalised and tested within Aptis. The focus of the analysis is on the extent to which the grammar and vocabulary items which constitute the Core component in Aptis are separable constructs.
Following this, the focus broadens to explore the extent to which we might consider the Core section as central to the construct of English language ability, as measured by all components of the Aptis test, including Listening, Reading, Speaking, and Writing.
A range of statistical techniques are applied to address these areas of investigation, including parallel analysis, generalised additive model for location, shape and space (GAMLSS), and multidimensional item response theory (MIRT).
The combined evidence from each of these investigative strands is shown to provide evidence to consider the Core component as indeed “core” to the Aptis test.