Paid Media Optimisation: Test Before Cutting Ad Spend

Summary

Use conversion reports to identify questions, rather than directly decide budget cuts.
Test a specific spending change and assess its effect on overall business results.
Allow for delayed purchases, seasonal demand, and uncertainty.
Weigh advertising savings against any lost profit before deciding what to cut.

Cutting a paid channel can save money, or it can quietly undermine results credited elsewhere.

A 2025 MIT working paper, analysing a game developer’s worldwide campaign data, found that paid advertising also contributed to installs classified as organic. Its findings show how an advertising report can miss part of a channel’s contribution: when someone sees or clicks an ad but later installs through an app store search, direct visit, or another unpaid path, the install may be recorded as organic even though the advertising helped generate it.

That does not mean every seemingly weak channel deserves its budget. It means the decision needs testing.

This guide explains how to assess a paid channel’s contribution to overall results, account for delayed sales and seasonal changes, and decide whether to cut, retain, or investigate further.

What Channel Attribution Can Tell You Before a Budget Cut

A channel receiving little conversion credit is a starting point for investigation. Trace the journeys you can observe: do customers encounter its ads before returning through paid search or another route? That pattern suggests a relationship worth testing, but does not establish that the earlier advertising caused the purchase.

IAB SEA+India’s discussion of retail media measurement highlights the value of connecting activity across platforms and online and offline environments. For budget decisions, those connections help frame a question: would overall purchases change if this channel’s spend fell?

Also, knowing how to measure marketing impact can help identify the broader distinction between credited sales and additional sales.

Define the Paid Media Budget Change You Want to Test

A useful question to guide a budget decision is: “What happens to total purchases if we reduce spending on this prospecting campaign while keeping other paid activities stable?”

Before choosing a test, specify:

The change: Which campaign’s budget will fall, and by how much?
The outcome: Will you assess completed purchases, qualified leads, or another business result?
The comparison: How will you estimate what would have happened without the reduction?

Measure the outcome across the business, where practical, rather than only the conversions credited to the changed campaign. Record other changes, such as prices or promos, that could affect the result too.

Choose a Method to Measure Paid Channel Performance

The IAB and IAB Europe’s 2025 measurement guidelines caution: “Not all methods are equal in their ability to establish causality”. The table below summarises how some such key performance measurement methods compare in their ability to determine causal relationships.

Method	What You Need	What to Watch For
Audience Holdout	Similar groups, ideally assigned at random, with ads shown to one group and withheld from the other:Assess purchases in both groups over the same period, using the same tracking method.	Tracking may miss purchases outside the platform. Stopping ads tests the effect of removing advertising entirely, which is different from testing what happens when you spend less.
Geographic Test	Regions with similar past sales patterns with ad budget reduced in some regions: Compare their sales with the regions where you keep the budget the same.	Differences between regions can affect results. People may also see ads intended for another region.
Marketing Mix Modelling	Historical sales and advertising data, plus information on prices, promotions, and other influences.	Results depend on the data and assumptions used. Since this is not an experiment, the model must be designed to assess how channels affect one another.

Choose the approach around the proposed change and the data available. Where tracking gaps limit the comparison, GrowthOps’ Performance Marketing and Analytics services include web and app analytics support.

Account for Delayed Sales and Seasonality in Your Test

Allow Time for Purchases

Customers may buy days or weeks after seeing an ad, and advertising can also continue to influence demand after spending falls. An early sales report may therefore miss part of the effect you are testing.

Set the test and follow-up periods around the buying cycle and the amount of data needed for a meaningful comparison. Know that there is no single test duration that suits every business.

Check Seasonal Changes

Seasonal changes can complicate the picture too. In its January 2026 retail-sales release, Singapore’s Department of Statistics attributed part of the year-on-year decline to Chinese New Year falling in February rather than January. This shows why calendar shifts matter when comparing sales.

Record promotions, price changes, and holidays alongside the results, so you can account for other influences on sales.

Use Test Results to Decide Whether to Cut Ad Spend

The findings can be used to assess three options:

Restore spending: If the test clearly shows a sales decline, compare the profit lost with the advertising savings. Restoring the budget may make sense if the lost profit is greater.
Keep the lower budget: If the savings outweigh any lost profit and the evidence is clear enough, retain the reduction and monitor results.
Investigate further: If the result is uncertain, check whether the test had enough data and time to detect a meaningful change.

Apply the decision to the campaigns and budget levels tested. A modest reduction does not show what would happen if you removed the channel entirely.

Paid Media Optimisation: What to Test Before Cutting a Channel