Ad Attribution Is a Black Box: How to Measure Ad Spend With MER
Anthony Nebel · 2 min read
In short
Tracking parameters get stripped before they reach your store, and Meta and Google each report a ROAS that credits themselves. So judge ad spend the old way: MER (total revenue divided by total ad spend), total revenue and new customers, tracked as a trend over weeks, with each change treated as a test you check against that trend.
Key takeaways
- Click IDs and UTMs get stripped or never sent, so the data your store sees keeps shrinking.
- Every platform reports its own ROAS, and they all count the same sale.
- MER is total revenue divided by total ad spend. No platform gets to grade itself.
- Make one change at a time, write down what you expect, then check total revenue against it.
- Targeting a 34 year old woman who likes red heels is over. The algorithm picks the audience now.
Marketing is heading into a black box.
The data you used to rely on is getting stripped out before it ever reaches you. And the platforms that are left all say the same thing: everything is going great.
So what do you believe?
Why attribution broke
Three things happened at once.
Tracking parameters get stripped. Apple’s Link Tracking Protection removes click IDs like fbclid and gclid from links in Mail, Messages and Safari private browsing. AI assistants send shoppers to your store with little or no campaign data attached. More and more of your traffic lands as “direct” or “unknown.”
The algorithm runs the account. Advantage+ on Meta and Performance Max on Google decide who sees your ads, where, and with which creative. You get the results, not the reasons.
Every platform grades its own homework. Meta counts the sale. Google counts the same sale. Add them up and your ad platforms claim more revenue than your store made.
Go old school: back to the 1990s
Before pixels and UTMs, brands judged advertising by one question: when we spent more, did the business grow?
That is where we are again. Three numbers do most of the work.
- MER (marketing efficiency ratio). Total revenue divided by total ad spend, across every channel. No platform gets to credit itself.
- Total revenue. From your store, not from an ad dashboard.
- New customers. Growth that only comes from people who already bought from you is not growth from ads.
Make educated guesses, then check them
Ten years ago you could tell Meta to find a 34 year old woman who likes red heels, and prove which ad sold the shoe. That precision is gone.
What replaces it is a habit:
- Make one meaningful change at a time: a new campaign, a budget increase, a new creative angle.
- Write down what you expect to happen to total revenue and MER.
- Watch the trend for two to three weeks, not two to three days.
- Keep what moved the business. Cut what only moved the platform’s own numbers.
It is less precise. It is also more honest.
The short version
Platform ROAS is a story each platform tells about itself. MER and total revenue are the scoreboard. Use the platform numbers to compare ads inside one platform, and use the scoreboard to decide where the money goes.
Filed under Paid social and ad creative