Attribution
Affiliate traffic
Also called partner traffic.
Affiliate traffic is visits sent by partners who earn a commission for sales or leads. The deal is performance-based, so attribution is the whole point.
How it is measured
Affiliate links carry a tag, often a partner id and a campaign. The site records the tag on landing and attaches it to any conversion in the credit window. The partner gets paid for the conversions the site credits.
Audit the tag against what the network reports. Differences usually come from link stripping, coupon sites that overwrite the click, or a different window. Settle on one counting rule before paying.
Worked example
A hiking-boot shop signs 14 affiliates. In September, one review blogger sends 1,780 sessions and 38 orders. A coupon aggregator sends 6,900 sessions and 61 orders.
The shop finds the coupon site's click appeared after the customer had already put boots in the cart. It changes the rule: commission only on first-touch referrals for new customers, and the coupon site's paid orders fall to 17.
How it differs
Affiliate traffic comes from partners paid per result. A UTM source parameter is the tag that identifies the partner. The traffic is a business arrangement; the parameter is just a label.
Common errors
Paying on last click without checking cart state. Using partner-supplied reports only. Letting tags lose case sensitivity. Forgetting to exclude self-referrals. Not agreeing on a window with the partner.
In practice
Write the rule for credit and window in the partner agreement. Cross-check each month's payout against your own logs. Drop partners whose clicks consistently appear late.