The merit list in the UPSC Civil Services Examination is determined by aggregating marks from both the preliminary and main examinations, followed by the scores obtained in the interview stage. Each examination stage is crucial; candidates must qualify the prelims to proceed to the mains, while the interview acts as a deciding factor for final placements. Additionally, the UPSC applies a standardized marking scheme, and any penalties for negative marking are reflected. This systematic evaluation process ensures that the most deserving candidates attain top ranks based on overall performance.