In psychology, we tend to be interested in individual minds rather than distributions. Most researchers theorise at the person level yet analyse data at the group level, creating the group-to-person generalisability problem, where group-level effects often fail to represent individual behaviour. My research assesses the extent of this problem by investigating whether group-level effects published in top journals generalise to a population majority, replicating key studies. In the second part, I develop practical tools to help researchers of all statistical abilities recognise and address this problem. Ultimately, my work aims to promote more accurate and transparent research practices across the social sciences.