GA4 - Item List & Promotion Attribution - SGTM Variable (Server)

Google Analytics 4 (GA4) has Item List & Promotion reports. But - no revenue or conversions are attributed back to Promotion or Item Lists. You have to do this attribution yourself.

This Variable for Server-side GTM makes it possible to attribute GA4 Item List, Promotion & Search Term to revenue or Ecommerce Events (ex. purchase) & Items.

Update: Any Item & Event scoped parameter can now be attributed.

• Last Click Attribution
• First Click Attribution
• Reset/delete Attribution Data after Purchase
• Attribution Time (for how long should Item List or Promotion be attributed)
  • Attribution Time can be either GA4 Session or Custom Attribution Time

This Template is available in the Google Tag Manager Template Gallery.

A similar Variable Template do also exist for GTM (Web). Differences between doing the attribution with GTM (Web) vs. Server-side GTM (SGTM) are listed below.

Functionality	GTM (Web)	Server-side GTM
Cross (sub)domain tracking	No *	Yes
Server to Server-side (Measurement Protocol)	No	Yes
Attribution/processing	Users browser	Server-side
Storage Limitation	Yes	No
Costs Money	No	Yes

* Cookies can do cross subdomain tracking, but are not very suitable due to very low storage capasity.

Attribution solutions

2 different solutions for handling the attribution are presented:

1. Firestore solution:
   • Firestore is a serverless, NoSQL document database from Google.
2. Stape Store solution:
   • Stape Store is a serverless, NoSQL document database from Stape.
     • If you are running Server-side GTM using Stape, Stape Store is recommended.

Firestore data example below.

Attribution explained

This solution can do either Last Click or First Click Attribution.

Attribution happens on 2 levels:

1. Event-level
   • Promotion without Items
   • Search Term
   • Custom Event Parameters
2. Item-level
   • Implemented Items data (ex. Item List name) trumps attributed Items data. Ex. if you are adding a Item to cart directly from a Item List, the implemented Item List Name will be used. If you are adding the Item to cart from a product page (where you shouldn't have a Item List implemented), the attributed Item List Name will be used.
   • Item Scoped Item List & Promotion attribution are independent of each other.

• Item-level trumps the Event-level.
  • Promotion without Items will not be attributed to a Item when Promotion with Items are attributed

To get a better understanding of the attribution, it's recommended to run some test scenarios where you inspect your own data:

• Run Server-side GTM in Preview Mode
• Look at the Firestore data being built or rewritten
• Inspect especially Items in GA4 DebugView

Last Click Attribution

With a Last Click Attribution model, this user journey illustrates the attribution:

1. User clicks on “Promotion 1 without Items” (promotion without any Items attached to the promotion). This is an Event-level promotion, and “Promotion 1 without Items” is the attributed Event-level promotion.
   • On the “Promotion 1 without Items” page, there is a “Promotion 2 without Items” promotion, and the user clicks on the promotion. This promotion is also an Event-level promotion. “Promotion 2 without Items” is now attributed to the Event-level promotion.
2. The user clicks next on a promotion for a bundled phone with earbuds package (“Promotion 3 with Items”). This promotion has 2 items attached, the phone and the earbuds. This promotion is attached to the 2 different Item Id’s (item_id = phone1 and item_id = earbud2) and is therefore an Item-level promotion.
   • User adds this bundle with 2 items to cart. The add_to_cart Event is attributed to the promotion.
   • User clicks after that on the “Users Also Looked At” Item List with other earbuds that it’s also possible to choose. The earbud (item_id = earbud3) the user clicked on is attributed to the “Users Also Looked At” item list.
     • On this page, there is also an “Users Also Looked At” item list. User clicks on the first selected earbud (item_id = earbud2). The earbud is now attributed to the “Users Also Looked At” item list, but is still attributed to the initial Item-level promotion. This because Item Lists and Promotion attribution are independent.
3. User completes the purchase, and GA4 adds some logic to the result, namely that Item-level trumps the Event-level.
   • The phone (item_id = phone1) is attributed to the “Promotion 3 with Items” promotion. The promotion didn’t have any Item List, so no Item Lists are attributed. If the promotion also had an Item List, this list would have been attributed.
   • The earbud (item_id = earbud2) is attributed to the “Users Also Looked At” item list, but in addition, since this item doesn’t have any Item-level promotion, the Event-level promotion “Promotion 2 without Items” is also attributed to the earbud.
     • Since Item-level trumps Event-level, “Promotion 2 without Items” is not attributed to the phone, since this has an Item-level promotion attributed.

First Click Attribution

In the same scenario, but using First Click Attribution, this would be the result:

1. Both the phone (item_id = phone1) and the earbud (item_id = earbud2) would both be attributed to the Item-level “Promotion 3 with Items” bundle promotion.
   • “Users Also Looked At” item list would also be attributed to the sale, since Item Scoped Item Lists & Promotion are independent.
   • None of the Event-level promotions “Promotion 1 without Items” or “Promotion 2 without Items” would be attributed since Item-level trumps Event-level.

Web implementation

To make the attribution work, also the implementation on the website must be correct. It’s especially implementation of Item List that can be incorrect.

All attribution in this solution is tied back to the following Events:

• select_item, add_to_cart (from a list) or select_promotion

When it comes to filling out the location_id parameter, if you don’t have Place ID as Google suggest using, fill this parameter with Page Path instead. Then you will get Page Path attributed as well.

The GA4 Event documentation allows for implementation of Item List and Promotion on both the Event-level and Item-level. This Template supports both implementations.

Promotion implementation

It’s recommended to implement all promotion parameters, but as a minimum for this attribution to work you must implement either promotion_id or promotion_name with the select_promotion Event.

Item List Implementation

The following Events should have Item List implemented. The rest of the ecommerce Events will read the Item List data using this Template.

• view_item_list
• select_item
• add_to_cart

Implementing Item List for the add_to_cart Event has though an exception. Item Lists should only be implemented if the Item is added to cart directly from an Item List.

You should never implement a Product Page Item List. The reason for this is that this will overwrite the Item List the user arrived from (ex. a “Related Products” list), and you will not be able to tell how well the “Related Products” list is working in terms of sales.

GTM (Web) Setup

To make the attribution work, the GTM (Web) setup must also be correct.

In the examples below, the setup handles implementation both on the Event-level and Item-level.

In the setup you will see that Data Layer is mostly Version 1. The GA4 Ecom Items - DLV Version 1 Variable Template is used for achieving that.

select_promotion & view_promotion

This setup handles both select_promotion & view_promotion, where promotion also has Event-level Item Lists. location_id is set to Page Path.

select_item & view_item_list

This setup handles both select_item & view_item_list, with Event-level Item Lists. location_id is set to Page Path.

add_to_cart & view_item

This setup handles add_to_cart & view_item. location_id in this setups is also Page Path, but Page Path will only be returned if item_list_name or item_list_id exist. Otherwise location_id will be undefined.

Solution by Knowit AI & Analytics (Oslo, Norway). Not officially supported by Knowit.