We’ve known that calculating reach and frequency metrics for Facebook is a tough engineering challenge, especially to do it in near real-time.
While Facebook has been vague as to which metrics are affected and to what extent, our guess is that the calculations of uniques by day and post are the main issue. Interactions, fans, and other aggregable metrics are easy to calculate– but deduping users across multiple sessions and devices is not.
Reach is really just unique impressions. And the sum of daily reach across a week is not the same as weekly reach, since people can see messages on multiple days. In the world of web analytics, we call this the non-aggregable metrics issue.
On February 25th, you can go into your analytics to see what’s changed.
Make sure you take a snapshot now, since they’re not going to keep the old, incorrect data for you.
Meanwhile, I’d rely upon other methods to analyze Facebook data via the graph API and ads data.
Dennis Yu
Dennis Yu is co-author of the #1 best selling book on Amazon in social media, The Definitive Guide to TikTok Ads. He has spent a billion dollars on Facebook ads across his agencies and agencies he advises. Mr. Yu is the "million jobs" guy-- on a mission to create one million jobs via hands-on social media training, partnering with universities and professional organizations.
You can find him quoted in major publications and on television such as CNN, the Wall Street Journal, Washington Post, NPR, and LA Times. Clients have included Nike, Red Bull, the Golden State Warriors, Ashley Furniture, Quiznos-- down to local service businesses like real estate agents and dentists. He's spoken at over 750 conferences in 20 countries, having flown over 6 million miles in the last 30 years to train up young adults and business owners. He speaks for free as long as the organization believes in the job-creation mission and covers business class travel.
You can find him hiking tall mountains, eating chicken wings, and taking Kaqun oxygen baths-- likely in a city near you.