Return on Ad Spend (ROAS) and Value on Ad Spend (VOAS) both refer to the same thing for us at Intentional: Return on your Investment (Ad Dollars).
We use ROAS in Ecommerce cases specifically where your Ecommerce platform provides our Analytics with actual Transaction Revenue figures. In these cases, we have a literal Return on Ad Spend.
We use VOAS more broadly where Goal Conversions don’t actually drive Ecommerce Transaction Revenue, but they do actually result in Value generated. In some cases, this Value may be actual (eg. A signup is worth $100) or estimated (eg. A PDF Whitepaper Downloader is worth around $75).
ROAS or VOAS = Total Conversion Value / Ad Spend