This paper tackles the question of methodological standards in public law scholarship, showing the perils of the current issues with access to relevant data and the promise of what can be achieved with better data and computational methods. It does so by focusing on the question of effectiveness of Cart challenges—the largest group of claims for judicial review in the High Court. Moreover, I discuss how the empirical question of effectiveness of judicial review is linked with the normative question of what counts as ‘success’. I show the perils of inattention to data limitations in the analyses of Cart claims by the Independent Review of Administrative Law and by the Government. I show the promise of better data and computational methods through my unprecedented empirical study of Upper Tribunal decisions that followed Cart judicial reviews. I find that the Government’s claim that Cart challenges are a disproportionate burden on resources lacks adequate empirical basis.