Attribution
UTM parameter
Also called campaign tag.
UTM parameter is a query parameter added to an inbound link to label it for reports. The standard set is source, medium, campaign, term, and content.
How it is measured
The values travel in the address after a question mark. The collector reads them on landing, attaches them to the session, and uses them in place of the referrer for channel labels.
Check for stripping. Some redirects and link shorteners drop or reorder parameters. Click your own tagged links and make sure the landing address keeps them.
Worked example
A sports-camp organizer shortens tagged links in text messages. 3,400 families get the message but analytics shows only 600 sessions with the tag. The shortener removes everything after the question mark on mobile.
The organizer switches to a service that preserves parameters. The next text brings 1,950 tagged sessions. The earlier untagged visits had been landing in direct and had made the text channel look weak.
How it differs
A UTM parameter is any one of the tag fields. UTM source is a particular one that names the origin. The parameter is the family; the source is a member.
Common errors
Tagging internal links, which overwrites the real source. Using spaces and symbols. Putting private data in the address. Not testing shorteners. Changing tags after links have gone out.
In practice
Tag only links that come from outside your site. Test each new link type end-to-end. Never put a name or email in a parameter.