Short answer
Attribution allocates credit to observed contacts; incrementality investigates additional sales caused by advertising. It needs a valid control comparison and equivalent outcomes. A call tracking report or growth over the previous month does not by itself establish that causal effect.
Key verification: Check group assignment, exposure, common sales outcomes and uncertainty estimates before interpreting a difference as an effect.
Sources and limitationsA customer seeing an ad before buying does not establish that the purchase depended on it. They may already know the business or need the service anyway. Attribution and incrementality answer different questions and require different evidence.
What each approach measures
Attribution relates an observed conversion to interactions under a rule. Incrementality compares outcomes with an estimate of what would happen without exposure. The Google Conversion Lift documentation distinguishes these measures and uses treatment and control groups.
Call tracking helps record origin and outcomes. It does not automatically create the counterfactual: callers following an ad may differ from visitors arriving through other routes.
A numerical example retaining its limits
| Fictional measure | Treatment | Control |
|---|---|---|
| Assigned people | 1000 | 1000 |
| Observed purchases | 40 | 30 |
| Purchase rate | 4% | 3% |
For these equally sized fictional groups, the difference is one purchase per hundred people, or ten per thousand. Relative growth against control is approximately one third. These are arithmetic operations, not a significance test or an actual campaign result.
Causal interpretation needs a design justifying comparison, controlling contamination and estimating uncertainty. Simply subtracting purchases is insufficient for groups of different sizes: appropriate analysis is required. A small difference and limited sample may be inconclusive.
Original pre-experiment worksheet
- Commercial decision depending on the result.
- Eligible population and group assignment method.
- Changed campaign and exposures to keep comparable.
- Common outcome: confirmed sale rather than a phone click.
- Period and follow-up of delayed purchases.
- Counts, observation losses and uncertainty method.
- Owner of design, analysis and data processing.
No universal minimum sample size can be substituted by this worksheet. Prepare the study with appropriate statistical knowledge and record analysis decisions before selecting favourable results.
Why before and after is insufficient
Months can differ through holidays, pricing, seasonality or service capacity. Switching off advertising and comparing two weeks introduces those differences. It may provide exploratory observations, but should not be labelled a randomised experiment or certain ad-caused sales.
Google states that Conversion Lift is unavailable for some accounts. Confirm eligibility and current requirements. A small business with few sales may need to postpone a formal study rather than produce a seemingly precise percentage.
Where CallRail fits
CallRail reporting may provide lead and attribution records if its markets and configuration fit the operation. That capability is different from automatic causal evaluation.
When recording study calls, keep sales criteria and follow-up access equivalent across groups. CallsIQ has not run this experiment or validated its sample; the example and worksheet separate attribution from a hypothesis about additional effects.
Sources and limitations
Documentary review: . Content type: Documentation-based guide with original resource.
Sources describe terms and capabilities stated by their owners. Proposed protocols and fictional examples do not establish product tests performed by CallsIQ.
- Google Conversion Lift documentationsupport.google.com
- Conversion Lift is unavailable for some accountssupport.google.com
- CallRail reportingwww.callrail.com
Check current terms
Consider these options if they solve the problem described. Confirm features, limits and availability in your country.
CallRail for international clients: its phone-number documentation lists availability in the United States, Canada, the United Kingdom and Australia. Spain is not on that list. Consider this option if you manage phone operations in those markets, and confirm numbers, destinations and terms with the provider. Availability checked on 2 October 2026.
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Official sources, explained calculations and clearly labelled examples. Read about our methodology and use of AI in writing.