ETF Correlation with a Index quoted in Yield

Is there anyway to measure a correlation between a ETF and a yield. Basically I’m supposed to compare muni etfs with with a specific index that just publishes a AAA curve everyday, but since they aren’t actual securities with a corresponding $Price, I can’t think of anyway to track how accurately this AAA curve index works as a proxy for actual muni returns.

any ideas out there?

Well, you’re either going to have to track historical returns for the ETF vs historical returns for the index, or you’re going to have to convert the index yield to a price (which is easier if it’s constant maturity).