Your guide to Google Ads attribution models & choosing the best type

Back in September 2021, Google Ads announced plans to gradually move away from the traditional last-click attribution model to data-driven attribution (DDA). Previously, DDA had only been available as an option to accounts with ‘enough’ data (or, to be rather cynical, accounts with a higher ad spend!).

On the surface, this all appears to be welcome news — at Extreme, we’ve been advocating for a move away from last click for a long time now. But how does DDA stack up compared to the other attribution models? And which should I plump for?

What is an attribution model?

Attribution modelling is the method used by Google to measure how effective a certain channel has been in a customer journey that led to a specific action being performed. The attribution model you use dictates how much credit is awarded to each touchpoint.

With more screens, more platforms and more connectivity, the modern customer hits multiple touchpoints and bounce between different stages of their journey before converting (as we explore in more detail in our guide to the new version of the sales funnel!).

Let’s see this in action.

Lucie’s vacuum cleaner breaks. Oh no, disaster! Dog hairs everywhere!

1. Lucie searches on Google for ‘best pet friendly vacuum cleaner’ and clicks through on a number of paid search ads for a few different sites including MyHenry, Shark and Dyson

2. Lucie navigates to YouTube to watch a video comparison about some of the top models and is hit by a MyHenry trueview YouTube ad before the video starts

3. Lucie continues to research across the web, visiting review and comparison articles in online publications such as Good Housekeeping. While on the Good Housekeeping site, she sees a dynamic retargeting ad, letting her know there’s a sale on the pet-friendly Henry that she looked at the other day. Lucie clicks through to see the deal for herself

4. Later that day, Lucie Googles ‘Henry Pet’, and clicks on a Google Shopping ad before going ahead and purchasing the vacuum. Lucie’s new Henry Pet arrives. She puts off hoovering for another two days.

That’s four potential touchpoints involved with the purchase of Lucie’s new cleaning companion. But which is awarded the credit for this sale? The attribution model you use will determine this.

What are the different types of attribution model?

Last-click, first-click, linear, time decay, position-based and data-driven are the six popular types of attribution model. Each applies different methods to apportion credit to the touchpoints involved in an action being performed.

So, using the aforementioned conundrum of Lucie’s vacuum cleaner, which touchpoints in the customer journey get a pat on the back? How would each model share out this conversion credit?

1. Last-click attribution model

This has traditionally been the default attribution model used by both Google Ads and Google Analytics. Last-click attribution awards 100% of the credit for a conversion to whatever click represented the final touchpoint. In the Henry Pet customer journey above, Google Ads would have suggested that the shopping ad was 100% responsible for the sale. None of the other touchpoints would receive any credit.

However, we know that this product sale wouldn’t have occurred without the previous three touchpoints.

2. First-click attribution model

As the name suggests, the first-click attribution model awards all of the credit for a conversion to the first known touchpoint in a customer journey. Applying first click attribution to the above example would determine that the initial paid click (which occurred following a search for ‘best pet friendly vacuum cleaner’) was the reason for the sale.

You might argue that this actually makes slightly more sense — Lucie would never have discovered the Henry Pet without that first search ad click. However, it doesn’t take into account the prompts and nurturing which helped her to her final decision. Without the YouTube and dynamic remarketing ads, she may have been swayed by another brand (perhaps one which has invested in this additional marketing activity!).

3. Linear attribution model

The linear attribution model is arguably a fairer method of measurement when multiple touchpoints are involved. While first- and last-click models award 100% of the conversion credit to one particular touchpoint, the linear model takes into account every single touch point and attributes an equal percentage to each. The linear attribution model would suggest, therefore, that every touchpoint is awarded 25% of the credit for the sale.

4. Time decay attribution model

The time decay attribution model assigns the highest proportion of credit to the most recent channel, and gradually moves down the conversion path, assigning a lower amount of credit to each. Using our vacuum example, this attribution model would assign the highest percentage of the credit to the Google Shopping ad, slightly less to dynamic remarketing, less still to the YouTube ad and the lowest percentage to the first paid search click.

5. Position-based attribution model

This model is a combination of the linear model and the time decay model. Position-based attribution apportions 40% of the credit to the first touch point, 40% to the final touch point, and then split the remaining 20% across all of the touch points in the middle.

Returning once again to our vacuum example, 40% would be allocated to the first paid search click, 40% would go to the shopping ad click, and 10% would be given to each of the two middle touch points. The benefit of the position-based model is that it takes every single aspect of a customer journey into consideration, whilst still enabling you to optimise around the most important parts of the journey.

6. Data-driven attribution model

Unlike the other five attribution models, there are no hard-and-fast rules to determine how conversion credit is awarded. DDA uses your own specific conversion data to calculate the actual contribution of each ad interaction across the customer journey. This means that each data-driven model is bespoke to each advertiser.

Because this model needs data in order to learn and calculate conversion credit, there are some eligibility requirements involved. For DDA to be a viable option, an advertiser must have a decent level of conversion data.

Which attribution model should you choose?

We hope that during the course of this article the scales have fallen from your eyes and you now see the benefit of selecting an attribution model that doesn’t give 100% of the credit to the last click before a conversion took place. Relying too heavily on a last (or first) click attribution model will all but ensure that certain channels or campaigns are undervalued and increases the likelihood that you will pause this ‘underperforming’ activity.

So if not first or last click, then which attribution model should you choose? If you’re using Google Ads, the chances are that your account has already adopted a data-driven attribution model. We advise you to make a note of the date of the change, and then see how this has affected your reporting.

However, if your account is not currently eligible for this change, it would be worth adopting a position based or linear model. You can change the attribution model manually in Google Ads by navigating to Conversions and then amending the model of each conversion action in your account.

Where to find attribution models in Google Analytics

The examples above relate to ways in which attribution models can be used to measure the effectiveness of campaigns in Google Ads. But can we use attribution modelling to measure the contribution of multiple channels and platforms in Google Analytics?

By default, Google Analytics uses a ‘last non direct click’ attribution model. You will almost certainly find that this type of attribution model favours paid search and shopping as well as organic search. This is due to many clicks and sales from these channels being brand searches, which will almost always appear as one of the final touchpoints in a customer journey. As a result, social media and display often end up being underrepresented.

To see how the adoption of different attribution models would impact the credit awarded to multiple channels in your Universal Analytics account, simply click Conversions > Multi Channel Funnels > Model Comparison Tool. If you have already made the switch over to GA4, click Advertising and then Model Comparison.

Need a helping hand with your paid media?

We have over 20 years’ experience developing results-driven paid media strategies for brands of all sizes and sectors. Take a look at just a small selection of the work we’ve been proud to deliver for our clients.

All it takes is a quick message or phone call to our team of digital marketing supremos to ameliorate your attribution model headaches.