British Journal of Educational Studies, ISSN 0007-1005 Vol. 51, No. 1, March 2003, pp 46–63 46 © Blackwell Publishing Ltd. and SES 2003 Blackwell Publishing Ltd Oxford, UK BJES British Journal of Educational Studies 0007-1005 © Blackwell Publishers Ltd and SCSE 2002 March 2003 51 1 000 Original Article WHAT IS MULTI-LEVEL MODELLING FOR? WHAT IS MULTI-LEVEL MODELLING FOR? WHAT IS MULTI-LEVEL MODELLING FOR? by Stephen Gorard, Cardiff University ABSTRACT: This paper is intended to be a consideration of the role of multi-level modelling in educational research. It is not a guide on how to design or perform such an analysis. There are several references in the text to sources that teach the practicalities perfectly well, and the tech- nique is anyway similar to other forms of regression and to analysis of variance. Rather, the paper describes what multi-level modelling is, why it is used, and what its limitations are. It does so in the hope that some readers will be enthused sufficiently to become appropriately critical ‘con- sumers’ of research using this approach, so building research capacity, and easing pressures on ‘specialist’ reviewers. Anyone who can read or perform standard multivariate analyses can understand, referee, or con- duct a multi-level model. Additionally, the paper makes three key points. The generally small sample size in each cluster at the lowest level of any multi-level model means that there is a danger of a greater bias in the results than in standard analyses that pool the data from all clusters. Even where there are genuine gains through the use of multi-level models these have to be set against a loss in simple intuitive grasp of the results, especially amongst policy-makers and practitioners. Therefore, long term, we are probably better advised to improve our research designs and the quality of the data we collect than to focus on more and more complex forms of analysis to overcome deficiencies in the datasets we already have. Keywords: multi-level modelling, research capacity building, regression, auto-correlation 1. Introduction Multi-level modelling (MLM hereafter) presents a particular chal- lenge for the capacity of the UK educational research community. It is growing in use as a technique, and widely cited as something that many more would like to know about (as shown by the results of a recent skills survey, see www.cf.ac.uk/socsi/capacity). Yet despite being around for twenty years now, it remains an obvious symptom of