Session Length As A User Engagement Metric


What is User Engagement?

What is app engagement or user engagement? In the mobile world, it generally refers to the frequency, intensity, and depth of interaction between a user and your app over a period of time. In other words, it is the level of user involvement with your app. How would you measure such a relationship? There is no one quantifying number, word, or sign to tell mobile app owners to what level the users are engaged with their app. App owners interpret different metrics coming together and come up with their own engagement mix.

What is Session Length?

One of the metrics app owners follow to measure user engagement is session length. Before diving into session length, let’s look at what a session is. A session represents a single period of user interaction with your app. It starts when the app is launched in the foreground, and it ends when the app goes to the background or when no events or interactions happen within a predetermined time interval. But it is important to keep in mind that mobile users perform multi-tasking. So, if a user leaves the app and comes back within a predetermined time, it could still be considered as one session. Hence, you would have different session definitions for different apps, verticals with different measurement partners.

Image: Lifewire, Typical multi-tasking nature of mobile users

For example, music streaming or other media-playing or recording apps, map-based apps such as Spotify, can still be actively used in the background. Hence, product managers must add background activity in the user’s session.

Based on the definition of a session and to put it in a general formula in which you define what inactivity is, the session length formula would be simply: 

Session length = (Time user becomes inactive) – (Time app is launched)

And to get the average session length, you would divide the sum of individual session lengths by the number of total sessions within a time interval.

Session length is an important metric to measure user engagement since it helps you understand how much a user spends in and interacts with your app. You can follow the user behavior and segment your users accordingly for optimized future user acquisition and re-engagement efforts.

Session length gives product managers valuable insight into the user experience. For example, session length can be used to correlate the time users invest in the app to the quality of the experience. It helps you understand the flow.  

Session length might be misleading when deciding whether your app is performing well in terms of engagement. Many might think that a longer session length is desirable. However, imagine having a ridesharing or taxi app. Long sessions imply that there might be problems with user experience, that the user is struggling with solving their problems quickly. Or imagine having a map-based app. The session length doesn’t necessarily depend on your app’s quality but might depend on your user’s travel habits.

Image: Localytics, This graphic might be an indicator of bad user experience for a taxi app but a good one for a social app.

Understanding the user expectation and behavior is critical in evaluating session length. Although mobile users, on average, spend around five minutes in an app, this number changes greatly for different app categories. Hence, instead of focusing on the general average session length, it is more important to follow the category benchmarks and historical and seasonal trends.

Image: Statista, Average app session length per user 2019, by vertical

According to the data from Adjust, in 2019, music app sessions were the shortest with 3.48 minutes worldwide. However, mid-core games app sessions lasted, on average, 38.47 minutes. Always make sure that you are comparing your metrics within your category.

Improving User Engagement by Measuring Session Length

Session length gives product managers the power to understand user engagement. Combined with other metrics, it shows whether your app’s mission is best served. Do your users leave too early without completing any tasks, or do they spending way too much time completing a task? You can discover the flaws in the user interface and improve it by removing or adding some elements.   

Make sure that there are no 0-length sessions. 0-length sessions might occur when a start or end session event is not sent or logged. So, check the unusual point in your session length data since app errors might be causing them.

Remember that although session length is a critical metric for user engagement, it is not the core goal of your business. Combine session length with other metrics such as session interval, time in-app, screen flow, etc. You can check the other user engagement metrics here.

If you are looking for ways to engage your users with your app content, you can use the power of in-app stories. Since the introduction of Snapchat, many social media giants adopted the story format and taught the users how they could use stories. Reaching the ideal session length, and eventually, improved user engagement is possible with in-app stories.

Image: Tarif Küpü, A recipe app using in-app stories

App engagement is important to assess the health of your app, and session length is one of the essential metrics to understand it. Use session length and combine it with other metrics to assess the quality of user experience and improve UX and user engagement.

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