I am interested in researching mathematics assessments, specifically how test questions work together to assess mathematical knowledge. This entails examining various aspects of test questions, such as the mathematical content embedded in them and the cognitive demand required to answer them correctly. My thesis project explores the relationship between question design and difficulty by analysing national and international test data. I aim to identify patterns between question features and student performance by analysing these data. My goal is to provide insights into the field of mathematics assessment, with implications for developing more effective and equitable assessment tools that can be used to infer mathematical knowledge validly.