What's a word that means "a single thing or a subset of things that could be used to represent greater overall trends"?
I work for a bookseller. The other day I was discussing a subset of several books that have consistently been bestsellers for the past few months. These books could be used to represent sales trends on a larger scale - something like "blue chip" books. In the conversation I referred to them as "bellwether books", but later on I doubted this was the correct usage of the word. "Bellwether" is defined as "an indicator or predictor of something". Is there a more appropriate word?