Engagement
Outbound link
Also called external link.
Outbound link is a link that leaves your hostname. Clicks on it send people away from your measurement.
How it is measured
The script compares the link's host with your own and records a click event before navigation. Because the next page belongs to someone else, that event is the only record you will ever have.
Tarsier does not capture outbound clicks automatically. Add its event call to partner and affiliate links, using the target host as the label.
Worked example
A travel blog links to hotel partners. Tracking shows 2,300 outbound clicks in a month, of which 1,100 go to one booking site. Another partner, linked only in the footer, gets 12.
The blogger moves the second partner into the body text, and clicks rise to 260.
How it differs
An outbound link leaves the site. Click tracking covers any click. A referrer is the same link seen from the receiving side. Only the first can be measured from your page.
Common errors
Missing subdomains that count as your own. Treating redirects through your own domain as outbound. Not delaying navigation long enough for the event to send. Ignoring links opened in a new tab by middle-click.
In practice
Review the top ten outbound targets each quarter and decide whether each earns its placement.