Attribution
Channel grouping
Also called default channel.
Channel grouping is a set of rules that rolls source and medium values into a short list of channels such as organic search, paid search, email, and social. It makes a long table readable.
How it is measured
Each rule matches on source, medium, or both, and the first matching rule wins. A session that matches no rule falls into an other bucket. Rule order matters.
Audit the grouping by pulling the source and medium pairs behind each channel. Check the largest pairs in each bucket and confirm they belong.
Worked example
A meal-prep service sees 11,300 sessions with 2,750 in the 'Social' channel. A look at the pairs behind it shows 940 sessions from a newsletter tool that tags its links with a medium 'social-share'.
Rewriting the rule so that medium 'newsletter' maps to Email moves those sessions to the right place. Social falls to 1,810 and email rises by 940, changing where the team puts its next hire.
How it differs
A channel grouping is the rule set. A source / medium pair is the raw label each session carries. The grouping hides detail to make comparisons possible.
Common errors
Trusting default rules. Leaving rule order untested. Tagging with free-form mediums. Not reviewing the other bucket. Changing rules without noting the date.
In practice
Export source and medium for last quarter and map each pair by hand once. Fix the rules that put pairs in the wrong channel. Annotate the date you changed them.