Rainey Reitman provides a helpful discussion of how your Facebook data is shared with Datalogix and how you can opt out. Here’s part of her explanation:
In order to assess the impact of Facebook advertisements on shopping in the physical world, Datalogix begins by providing Facebook with a (presumably enormous) dataset that includes hashed email addresses, hashed phone numbers, and Datalogix ID numbers for everyone they’re tracking. Using the information Facebook already has about its own users, Facebook then tests various email addresses and phone numbers against this dataset until it has a long list of the Datalogix ID numbers associated with different Facebook users.
Facebook then creates groups of users based on their online activity. For example, all users who saw a particular advertisement might be Group A, and all users who didn’t see that ad might be Group B. Then Facebook will give Datalogix a list of the Datalogix ID numbers associated with everyone in Groups A and B and ask Datalogix specific questions – for example, how many people in each group bought Ocean Spray cranberry juice? Datalogix then generates a report about how many people in Group A bought cranberry juice and how many people in Group B bought cranberry juice. This will provide Facebook with data about how well an ad is performing, but because the results are aggregated by groups, Facebook shouldn’t have details on whether a specific user bought a specific product. And Datalogix won’t know anything new about the users other than the fact that Facebook was interested in knowing whether they bought cranberry juice.
Read more on EFF.