UPSC determines the merit list for candidates based on their performance in the written examinations (Mains and Prelims) and the Personality Test. The scoring system ranks candidates, with higher scores leading to better placements in the merit list. Important factors include the examination difficulty level, the number of candidates appearing, and performance trends. The commission also considers reservation policies and category-based adjustments in creating the final list. Transparency and fairness in the evaluation process are emphasized to ensure that the most qualified candidates are selected for various civil services.