Publishers that rely heavily on referral traffic from Facebook had a bad day last week when the social network announced that it was changing its News Feed algorithm to emphasize posts from friends and family over the news.

Those concerned about the change should brace themselves, because data indicates that it may not have taken effect yet.

That's according to analytics company Parse.ly, which on Thursday published the findings from a survey of data from more than 600 of its digital publishers. The takeaway: It's still too early to tell if the change is causing referral traffic to drop:

...Many of Parse.ly’s clients have already reported seeing a general decline in referral traffic from Facebook over the weekend; they are concerned that Facebook’s algorithm changes have already started to negatively impact their expected site traffic. However, it is still not clear if Facebook actually took the changes live, or if these slight decreases in activity were due to a seasonal dip in traffic due to the Fourth of July weekend. (The holiday weekend is a more likely explanation.)

The number crunchers at Parse.ly created a graphic that compares actual pageviews per minute from Facebook with projections of that same metric based on pre-announcement data. It shows that the numbers are relatively similar, with current pageviews actually eclipsing the expected number as of this afternoon:

(Screenshot, Parse.ly)
(Screenshot, Parse.ly)

In its announcement last week, Facebook did not say specifically when the changes to News Feed would begin to take effect. Lars Backstrom, Facebook's engineering director, said the tweak would be rolled out "over the coming weeks" in one of the company's semi-regular "News Feed FYIs."

Timing aside, there changes to News Feed will produce clear winners and losers among news organizations. Those who will emerge relatively unscathed, according to Digiday: Organizations that produce shareable stories, publish lots of video and upload lots of content directly to Facebook. The losers include mid-size publishers and anyone that hopes to lure big audiences by publishing straightforward breaking news.

The magnitude of the changes has been forecast as important but not apocalyptic. Adam Mosseri, the head of News Feed, said the change would be "significant" but not "humongous" in an interview with CNN last week.

Facebook did not respond to a request for comment.