I'm writing a research paper on the economic impact of the Black Death in 14th century Europe, and I keep encountering contradictory data on population decline rates from different regions. How can I effectively reconcile these discrepancies to present a coherent analysis?

I've gathered data from sources like chronicles and demographic studies, but estimates vary widely—for example, some say England lost 30-40% of its population, while others cite 50-60%. I need to understand the methodologies behind these numbers and how to weigh their reliability without oversimplifying.