Admission to Master's degree in Data Science without a STEM Background?
You said that you were studying Economics, wouldn't that be considered a STEM area (or at the very least, certain segments of Economics). I know that for instance, financial economics have been considered a STEM subject by certain institutions (e.g. Columbia)

Having that said, it really depends on the program that you are applying to. I've seen people from a broad spectrum of backgrounds enter into what would traditionally been known as quantitative sciences. I've seen psychologist and linguists working at an engineering departments for instance. What I would do is to consult the person in charge of the program that you are interested in, and ask about the specific requirements. From your own perspective, it would certainly help to take on additional courses that deal with data science so you have some experience with it, even if your primary degree isn't in a "STEM" field.