Floodlight recognizes users by their cookie ID or device ID, which becomes the user ID. Floodlight records the user ID after any impression, click, or other activity that results in a call to our servers and this information can be used by Floodlight for conversion attribution. When there isn't enough information for conversions to be observed directly, Google uses conversion modeling to estimate them.
Keep in mind that user IDs are associated with browsers or devices, not people. If a person uses multiple devices, such as a phone, a tablet, and two different browsers on a laptop, each device or browser is identified separately. Similarly, if people share a computer or a device, a single user ID might represent multiple people. So if someone views your ad in Chrome, then visits your website in Firefox, Floodlight will have no way of associating the ad impression with the visit to the Floodlight page, even though both events took place on the same computer.
Due to differences in cookie and device ID settings, advertisers may see fluctuations in delivery and performance when cookies or device ID are unavailable.
Despite these limitations, Floodlight has plenty of useful data to work with and is still a powerful tool for helping you to understand the effectiveness of your campaigns.