Mixpanel funnels automatically backfill event properties to reflect the most recent value of a property. Funnels also automatically forwardfill event properties if they are absent in susequent steps. Understanding how properties forward and backfill will facilitate a deeper understanding of funnel segmentation, maximizing the value that funnels have to offer.
For more information on Funnels, visit the funnels deep dive article.
Mixpanel “forwardfills” event properties in instances where properties are sent in earlier steps of a Funnel but not sent in subsequent steps of the same funnel. This means that the property that is present in early steps of a funnel is appended to the later steps of the funnel where it was previously absent.
For example, say that the user is shopping on your website and you want to track a funnel from Log In to Purchase. There are three events in this journey: Log In, Item View, and Purchase. Each event has its own properties, and the “Name” property is only sent with the “Log In” event. This property will be added to the subsequent events, where it was previously absent:
As you can see in the diagram above, the property of “Name” is only a property for the event “Log In”, but that property is forwardfilled to the subsequent events.
Mixpanel “backfills” event properties in instances where properties are sent in later steps of a Funnel but not sent in the earlier steps of the same funnel. This means that the property that is present in later steps of a funnel is appended to the earlier steps of the funnel where it was previously absent.
For example, the user shopping on your website chooses to buy a shirt that costs $5. In this instance, properties of the item that is purchased are not sent until the “Purchase” event, so the property is backfilled and added to the “Item View” and “Log In” events:
As you can see, the property of “Item Price” is only a property of the event “Purchase”, but that property backfilled to the previous two steps. Also, the properties sent with the event “Item View” are backfilled to “Log In”.
Backfilling Event Property Values
If an event property is sent with all steps of a funnel but the value of the property changes across steps, then the most recent value is applied to all steps of the Funnel.
For example, the user shopping on your website views a blue shirt and adds it to their cart. However, when they make their purchase, they have changed their mind and decided to get a red shirt instead:
As you can see, the property of “Item Color” is Blue for Event 2, but changes to Red for Event 3. As a result of backfilling, the property of “Item Color” will be appended to Red in the “Item View” event, and further backfilled to “Log In” as well.