Milanovic, 2009; Weir, 2005). Establishing the relationship is also not a one-off activity, but rather involves the accumulation of evidence over time (e.g. it needs to be shown that test quality and standards are maintained). Cambridge ESOL has been working since the 1990s to refine its understanding of the relationship between its different assessment products, including IELTS, and the CEFR. The relationship of IELTS with the CEFR is complex as IELTS is not a level-based test, but rather designed to span a much broader proficiency continuum. It also utilises a different 9-point band scoring system; thus, there will not be a one-to-one correspondence between IELTS scores and CEFR levels. It is important to bear in mind the differences in test purpose, test format, test populations, and measurement scales when seeking to make comparisons. With the above in mind, Cambridge ESOL has conducted a number of research projects since the late 1990s to explore how IELTS band scores align with the CEFR levels.  A number of these were summarised in Taylor (2004b), while cautioning that, "As we grow in our understanding of the relationship between IELTS and the CEFR levels, so the frame of reference may need to be revised accordingly." Note that the IELTS band scores referred to in Figure 1 above are the overall band scores, not the individual module band scores for listening, reading, writing and speaking. It is important to recognise that the purpose of this figure is to communicate the relationship between IELTS and the CEFR.