The odds ratio, i.e. at equal mathematics and science proficiency, how many times higher is the probability of repeating an academic year for a student from a more disadvantaged background compared to a student with more resources. For example, a value of 4 means that, with equivalent skills in mathematics and science, a student with fewer resources (25% of students with fewer resources) is four times more likely to have repeated an academic year than a student from a more favourable background (25% of students with more resources).