Bachman & Palmer Construct validity pertains to the meaningfulness and appropriateness of the interpretations that we make on the basis of test scores. The contrast validity is used to refer to the extent to which we can interpret a given text score as an indicator of the abilities, or constructs, we want to measure.
IELTS has 9 band scales to evaluate the ability for students who are going to the speaking countries. A score is reported each model of the test. The individual module scores are then calculated to produce an overall band score. Each band scales represent the various English levels of learners. The description of the scores is stated as following table (IELTS Official Website):
9
Expert user
Has fully operational command of the language: appropriate, accurate, and fluent with complete understanding
8
Very good user
Has fully operational command of the language with only occasional unsystematic inaccuracies and inappropriacies. Misunderstanding may occur in unfamiliar situations. Handles complex detailed argumentation well.