Misleading parameter names

[gvegayon]

[nitpick] Misleading parameter name: The parameter prevalence is used for both proportions and absolute counts depending on the as_proportion flag. When as_proportion is false, the parameter represents counts, not prevalence. Consider renaming to values or counts_or_proportions to better reflect its dual purpose, or add a clarifying note in the documentation.

Originally posted by @Copilot in #133 (comment)

[olivia-banks]

I'll tackle this inside #92, since I'm changing a bunch inside there. Assigned to myself.