Introduction

The upsurge of interest in research on the age factor in foreign language settings in recent decades has raised new methodological and assessment issues. Although much research has been devoted to identifying age effects and to their interaction with social-psychological, personal and affective variables, the specific impact and contribution of different quantitative approaches has more often than not been disregarded. This is surprising, considering that methods in age research have evolved significantly over the past couple of decades, and that it would therefore not have been unrealistic to expect certain methodological innovations to have entered this domain. Multilevel modelling (MLM) – a subgroup of linear mixed-effects regression modelling – has for some time been finally finding its way into certain SLA subfields. Research on the age factor, however, has only recently – and tentatively – begun to adopt these kinds of statistical models.

This chapter discusses the benefits that MLM can furnish to any SLA research that involves the sampling of populations, within educational establishments or naturalistic settings, and that has a particular focus on chronological age and the age of onset of acquisition in their roles as continuous and categorical predictors. Since the emphasis here is on conceptual issues and practical recommendations, technical details are deliberately kept to a minimum and mathematical details of the methods in question will be avoided.

First, we explore some central issues in the age factor discussion, following up on van Heuven's discussion in Chapter 5. Secondly, we review methods that have developed in respect of linguistic approaches to the age factor in SLA and go on to outline the benefits and advantages of mixed-effects models, in particular regarding perceived gaps in age-related research. It is hoped that this discussion will contribute to ensuring the consistent choice of the most insightful analysis in relation to any given dataset.