When analyzing a Metric in FullStory, you will see Advanced Options under the "Compare users" and "Group by" filters.
Clicking on Advanced Options allows you to adjust the Segment Scoping Options for your Metric.
If you select the option to count events performed "By the matching users", Metrics will be counted for all users from the Segment whenever they meet the Metric criteria in any session within the specified time range.
If you select the option to count events performed "Within the matching sessions", Metrics will be counted only when users meet the Metric and Segment criteria within the same session. This is the default setting for metrics in FullStory.
Segment Scoping Example
For example, let's say your company is promoting a blog post to drive traffic to your site and encourage users to complete a task. You want to measure the impact of this blog post.
One way you could measure the success of the blog post is to count the number of users that view the blog and at some point also completed the task, whether in the same session or not. You could accomplish this in FullStory by creating a segment of users that have visited the blog post and then creating a Metric counting the number of unique users that completed the task. Since you want to know the number of users that viewed the post and at some point also completed the task, you would select the "By the matching users" option from the Segment Scoping Options.
Another way you could measure the success of this blog post is to count the number of users that view the blog post and also completed the task in the same session. You could accomplish this in FullStory by creating a segment of users that have visited the blog post and then creating a Metric counting the number of unique users that completed the task. Since you want to know the number of users that viewed the post and completed the task in the same session, you would select the "Within the matching sessions" option from the Segment Scoping Options.
Another example could be if you were interested in understanding Mobile users on your site.
When using the Mobile segment, if you selected the "By the matching users" option, this will target events from user sessions where the user was ever on mobile during the segment time range. So if they had one mobile session and one desktop session in the past 30 days, events from both sessions would be considered for the Metric calculation.
On the other hand, if you selected "Within the matching Sessions", this will target events from sessions where the user was on mobile. So if they had one mobile session and one desktop session in the past 30 days, only events from the mobile session would be considered for the Metric calculation.
Time Period
Keep in mind that both a Segment and a Metric give you the ability to define a Time Period. If you are using different time frames for your Segment definition and your Metric definition, it is important to understand how that will impact your Metric results.
If you're using the "By the matching users" option, the results will be limited to the Metric's time period, but the users included in the calculation include all who matched the Segment's time range.
If you're using the "Within the matching sessions" option, the results will be limited to sessions that meet both the Metric and Segment criteria, so it's best to user the same time period for your Metric and Segment.
As a note, if your Metric is using a Segment that has a custom time period, FullStory will automatically scope your Metric to count events performed "By the matching users" for you without you having to make any adjustments.