Science is not just about formulas and theory's, in essence its about the gathering of facts that we both know to be true and can prove to be true.
Anthropology is an older form of science, while many fields of study have changed dramatically over the years. Anthropology remains largely the same now as when it was created. Its all about learning about humans, how we evolved and how we have developed culturally, socially etc..
Its a difficult thing to explain, have a look at the site below and come to your own conclusion:
But tends to more of an art/literature. That's because it represents literary pieces of art, which help us understand other people of our kind, mankind. Scientific formulas apply to all time, I mean they're linear (A causes B). However, anthropological studying results constantly change. There is no rule or formula that is surely applies to all cultures. Plus, anthropology includes creative activity, the art of observing and interacting and understanding other cultures. Therefore, I believe anthropology is a literary art.