<p>For over a century, research has shown that human perceptual decisions are systematically influenced by prior perceptual experiences, a phenomenon known as serial dependence. It has recently been suggested that serial dependence can improve perceptual decision-making by mitigating uncertainty and reducing variability in perceptual estimates—leading to a superiority effect. However, this claim remains largely untested. Here we present a large-scale analysis, compiling the most extensive dataset of serial dependence studies from the past decade. Contrary to the proposed superiority effect, our findings indicate that serial dependence deteriorates rather than improves perceptual decision-making. These results challenge prevailing models and emphasize the need to rethink serial dependence and its role in human perception, cognition and behaviour.</p>