"And I think, we are not 100 percent perfect – other platforms aren't either – but we want to be held accountable and we will put our hands up, we will tell you what's gone wrong and then we'll take the appropriate action, and it might cost us in the short term," she said.
Facebook now has 24 measurement partners and in March, it opened up its advanced measurement tool to more advertisers, not just the largest ones.
Mendelsohn added that Facebook is "obsessed" with how technology can drive business growth, and urged brands to have effective digital and mobile strategies, criticizing advertisers for simply putting adverts made for TV on to the platform, without considering viewers' very short attention spans, especially on mobile.
Speaking to CNBC by phone following a speech she made to an internet conference in Amsterdam this week, she said:
"(There is) general agreement from everybody now that mobile has radically changed the way in which people are discovering, sharing and experiencing content and especially video content. Businesses are struggling to keep up and that's actually a major disconnect that is causing greater disruption across industry," she said.
On average, people spend 1.7 seconds looking at content on their Facebook news feed on their smartphones, but this figure multiplies by five for videos, Mendelsohn added.
She said there are variety of ways that people watch video on mobile, including on the go, "when you've got short moments where you are probably multi-tasking," the "lean-forward moment," when someone ends up in a "rabbit hole" of content, and "lean back," where someone might watch an episode of a show.
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