YOY Calculation

[rohitraturi]

I am doing a YOY % change in the billed amount. I want to get the data for year 2015, 2016 and 2017. I am able to filter the data based on year. This is the expression I am using.

sum({<correction = {'N'}, [denial code] = {"*"}, payamt = {0.00},postingdate = {"year(postingdate) = 2015"}>} chgamt)