Word Meaning “A single thing that's an indicator of greater overall trends”?

Question

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?

Answer 1

Bellwether seems like an excellent usage for the situation you describe, because when you're talking about trends (at least, other than retrospectively) you're somewhat inherently talking about prediction. If prediction weren't relevant to the situation I might use exemplar or typifier, or perhaps something like quintessential example if I were wont to wax verbose.

Those are all for a single item; for a subset of items, representative sample comes thundering out of the land of statistics to dominate the lexical landscape.