First, here's a look at the Chrome Extension (if you want it, go get it here!):
The above example is for crowdtangle.com, and it shows some the folks who have shared links to our site on the public social platforms we track. Everything under "Top Referrals" comes from CrowdTangle data and is the same information you would find in any of our other products.
However, the top bar -- Facebook Interactions -- comes from a different place within Facebook. It is meant to represent how many interactions a URL has gotten across all of Facebook, not just public posts; it even includes shares via Messenger.
Sharp-eyed readers will notice that in this example, the "Facebook Interactions" section features fewer interactions than the total interactions listed in "Top Referrals"! How can that be?
The answer is that the data comes from different sources, and we have different ways of calculating things. We at CrowdTangle don't have any control over the numbers that drive the totals row; what we do know are two things:
Any changes to a website or the canonical URL (e.g. moving from http to https, or changing the address after it has gone live) can make it seem like the site is an entirely new webpage that starts aggregating anew. In the case of moving from http to https, Facebook Interaction numbers will be higher than Top Referral numbers, because Facebook restarts aggregation when the change occurs, but CrowdTangle continues to aggregate data. In the case that the URL itself changes after the link has gone live, CrowdTangle will miss interactions for posts using the old URL.
Certain URLs are not treated in such a way that they add their numbers to the Facebook Interactions total. We don't have information as to why.
But here's what we do know: You can be certain that the bottom totals are accurate based on the posts we're tracking within CrowdTangle. We have them all in our system and can show them to you.
As for the top Facebook Interactions section, treat it as a reasonable estimate (in most cases) that can be directionally helpful, but whose numbers we don't control and can't guarantee.