NEW YORK (AP) — The crisis-management playbook is pretty simple: Get ahead of the story, update authorities and the public regularly, assume responsibility and take decisive action. Crisis-management experts say Facebook is 0-for-4.

Facebook's two top executives, CEO Mark Zuckerberg and chief operating officer Sheryl Sandberg, have gone radio silent since news broke on Sunday that political consulting firm Cambridge Analytica may have used data improperly obtained from roughly 50 million Facebook users to try to sway elections, including the 2016 White House race.

Meanwhile, Facebook users have been leaving the social network or mulling the possibility , and Facebook's stock is down 9 percent since Friday.

Facebook's handling of the growing public-relations crisis is remarkable in that one of the world's biggest companies seems not to be playing by well-established crisis-management rules.

"This will go down as the textbook case study as how not to handle a crisis," said Scott Galloway, a New York University professor of marketing. "The only thing we know about this and are comfortable predicting is that it's going to get worse."

Zuckerberg is likely to speak soon. A person familiar with the matter who was not authorized to discuss it publicly and spoke on condition of anonymity said Wednesday that Zuckerberg planned to speak sometime within the next day with a "focus on rebuilding trust."

It's likely the delay was due to top brass working out legal aspects of the Cambridge Analytica case. But that doesn't matter to the public.

"It's likely they are trying to coordinate a careful response, but each day of silence costs them more losses in terms of public trust," said Safiya Noble, assistant professor of information studies at the University of Southern California. "This is translating to economic losses too, so the silence is not insignificant."

"At this point, 'Why did you wait so long to make a statement?' is now news in itself," added Paul Argenti, a business professor at Dartmouth.

Most Fortune 500 companies adhere to well-established crisis-management rules. When video surfaced of a passenger being dragged from an overbooked United Airlines flight last April, for example, CEO Oscar Munoz at first hedged but then apologized . When Pepsi ran an ad last spring featuring Kendall Jenner that appeared to trivialize the "Black Lives Matter" movement, the company pulled the ad , saying, "Clearly we missed the mark, and we apologize."

The point is to at least make an effort to seem remorseful to win back public trust, experts say. But despite user outcry on its own Facebook page and a call from Congress for Zuckerberg to testify about Facebook's role in election-meddling, Facebook seems to be charting its own course.

It's a pattern Facebook has long followed, said Helio Fred Garcia, a professor of crisis management at NYU and Columbia University in New York. Facebook hedged during its early days in 2007 over a controversial advertising program called Beacon that did not alert users it was sharing their activity, and it did so again in its response to Russian bots hijacking Facebook ad software during the Trump campaign in 2016.

"Facebook has been too late. Facebook has done too little and has been too legalistic" each time, Garcia said. "I have yet to find a crisis Facebook handled that I could stand in front of crisis management classes and say, 'Here's an example of how to handle a crisis.' They've never been able to handle a crisis."

Once Zuckerberg addresses the public, the PR flap may eventually be forgotten. But it will take a lot longer than if the company had addressed public concerns immediately, Garcia said.

"It's much harder to restore trust once it has been lost than to preserve trust before it has been lost," he said.

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This story has been corrected to show that Facebook's ad program was 2007, not 1997.