Advanced Segments: Should I filter by Sessions or Users?

To filter by Sessions or by Users? That is the question… at least it is if you have ever configured an Advanced Segment in Google Analytics.

Advanced Segments are a powerful tool for “slicing and dicing” your analytics data, allowing you to isolate and analyze subsets of sessions or users. The choice between sessions or users however, can have a significant impact on the data that gets captured by your segment. Thus, it can have a significant impact on the insights and conclusions that you may draw from your analysis.

Let’s take a look at the difference between session-based and user-based advanced segments, so that no matter what analysis question you are trying to answer, you will know exactly which type of segment to use.

Consider the following scenario where a single person (let’s call her Alice) visits your website three different times:

1. Alice arrives at your site from a Google search. Makes a purchase. Signs up for your monthly newsletter. Leaves site.
2. Alice arrives at your site from a link in your email newsletter. Makes a purchase. Leaves site.
3. Alice arrives at your site from a link in your email newsletter. Watches a video. Leaves site.

Now let’s say you create an advanced segment to analyze “Email Visitors”, people who have arrived to your site from your email newsletter. Assuming that you have tagged the links in your newsletter with appropriate campaign parameters, you can use the source, medium, or campaign dimensions to define this segment (e.g. medium = “email”).

Consider the following two segments:

• Segment U: Filtered by users, the segment will capture all of Alice’s sessions, since in at least one of her sessions she has arrived from the email. Thus, this segment includes 1 user and 3 sessions.
• Segment S: Filtered by sessions, the segment will capture only Alice’s 2nd and 3rd sessions. At the session-level, only #2 and #3 are from the email. Thus, this segment includes 1 user and 2 sessions.

In this case, the difference between session-based and user-based segmentation is one-third of your data!

Let’s say you then wished to look at conversion rates for this segment of email visitors. Specifically, you want to know what percentage of people completed a purchase:

• In Segment S (which includes Alice’s sessions #2 and #3), only in session #2 did she make a purchase. So the conversion rate would be 50% (1 out of 2).
• In Segment U (which includes all 3 of Alice’s sessions), the conversion rate would be 66.6% (2 out of 3), since Alice made a purchase in sessions #1 and #2.

50% vs. 66% is a significant difference! Let’s just take the higher number, right?

WRONG!

If you are using Advanced Segments for any kind of analysis, you need to understand the implications of session vs. user-based segmentation.

We have used a single user as an illustration, but when extended to hundreds, thousands, or even millions of users and sessions, the scope of your advanced segment can have a significant impact on the results of your analysis.

So, which is the right choice?

Well, it depends on what you are aiming to measure and analyze.

What’s more important is that you are able to accurately describe exactly what your segment is capturing:

• Segment S captures all sessions originating from an email link.
• Segment U captures all sessions from users who arrived from email in at least one of their sessions.

If you are interested in assessing the ability of your email newsletter to directly generate conversions, session-based Segment S may be more relevant. But if you are more interested in the people who clickthrough from the newsletter, user-based Segment U may be more relevant.

Thus, the right choice is always relative to the question that you’re trying to answer.

What kinds of analysis do you use Advanced Segments for? Have you ever been confused by the data that GA shows you? Let us know!