What's behind the success of Netflix's latest releases?

Sex Education, Bird Box and You have been a big success for Netflix

If you've spent the last few weeks binge-watching endless hours of TV (and finishing off leftover Christmas Twiglets) then you're in very good company.

On Thursday, Netflix published the figures for some of their biggest recent releases - Sex Education, You and Bird Box.

And those numbers were pretty impressive, with the two series on course to be watched by 40 million accounts by the end of the month.

Bird Box, which features Oscar-winning actress Sandra Bullock as the lead, has already passed more than 80 million views.

Going viral on social media

You has been a huge success on Netflix

You, which is based on Caroline Kepnes' best-selling novel of the same name, was initially made for the Lifetime Network in the US, but only averaged about 611,000 viewers.

Its addictive format, which sees psychopath bookshop owner Joe Goldberg stalk love interest and college student Guinevere Beck, had Netflix viewers hooked - and more importantly, talking about it all over Twitter.

The series sparked a huge debate online over whether it was acceptable to empathise with Joe, so much so that the actor who plays him, Penn Badgley, had to remind people he was a murderer.

Buzzfeed's TV editor Scott Bryan tells the BBC the combination of "Netflix's international appeal and social media influence" helped spread You a lot further than the Lifetime Network could.

"If you'd have told me about You six months ago, then I wouldn't have known where to find it, but with Netflix's good marketing and social media, I could," he says.

This picture of Sandra Bullock turned into a viral meme on Twitter

Bird Box also enjoyed similar social media success, with its star-studded cast of Sandra Bullock and Sarah Paulson and thrilling plot drawing in viewers.

TV critic Emma Bullimore references the "Bird Box memes and viral social media campaign" that flooded Twitter over Christmas.

• Bird Box drives Netflix subscribers to 140m

• 'My sleepless nights over Sandra Bullock's blindfold'

"Bird Box isn't Citizen Kane, but it has incredible talent and is based on an intriguing concept," she says.

"I saw the blindfold pictures all over Twitter so thought 'let me check this out'."

Sex Education was late to the party with its January release date, but it too is set to reach 40 million viewers by the end of the month.

The show follows a British sixth-form student, who opens up a sex therapy clinic to help his clueless classmates. It's resonated with many of Netflix's younger subscribers, whilst some of its wittiest lines have become popular memes on Twitter.

"With Sex Education, British comedy has always had international appeal and that has been a driver for this series, and the fact there aren't many shows like it at the moment," Bryan explains.

"Also it's got Gillian Anderson in it and a universal youthful appeal - I've seen it shared so many times on social media.

"Plus it's well-written, thought through and really inclusive on LGBT representation and serious subjects," he adds.

The Christmas effect

Asa Butterfield and Gillian Anderson in Sex Education

Another important factor is the time of year - these releases all came out in late December and early January.

Bryan tells the BBC: "Christmas is when people start a lot of shows and catch up", and adds that these releases really capitalised on that.

"For example, Netflix released Black Mirror's Bandersnatch just after Christmas and people were watching it with their families."

Bullimore also thinks downtime has played a part in impressive viewing figures.

"People have a lot of time over Christmas and want to find something new to binge watch, so bored Netflix subscribers want to find something to get obsessed with," she tells the BBC.

"You is a thriller and it grabs you and forces to watch the next episode."

Why has Netflix released these figures?

Sandra Bullock's character learns the significance of birds in Bird Box

At the end of December, Netflix tweeted that more than 45 million Netflix accounts had watched Bird Box - the best first week ever for a film on the service.

This was the first time that we were given any indication of how shows and films are received on the network, and Netflix were clearly proud of these figures.

"I think it's a bit of publicity to further their own advantage," says Bullimore.

"They're really interested in their industry status, on getting Emmys and being involved with the big players so they get Hollywood stars on the network."

"[Releasing these figures] shows the global power Netflix has," says Bryan.

"They make shows that can be watched in 195 countries at the same time and this is something rivals can't do."

Emma Mackey and Asa Butterfield are two of the stars of Sex Education

Bryan thinks that while these figures appear impressive, it's difficult to really measure their relevancy.

"What I'm trying to get clarity on is what counts as a viewer. In a shareholder letter yesterday they counted a viewer as watching 70% of one episode; you don't see who drops off [and doesn't watch the rest of series].

"But if you looked at BBC figures for Killing Eve and Bodyguard you could see how many people were watching each episode."

Bullimore adds: "Netflix's viewing figures have always been shrouded in mystery, they won't tell us how many people are watching but the rest of the TV industry relies so heavily on these figures.

"Now suddenly after saying no, they're very willing to, but they are calculated in a different way, therefore a straight comparison is very difficult."

But Hollywood Reporter said Netflix's content chief Ted Sarandos said the decision beind revealing some of its viewing figures was to share "cultural metrics".

He added that in his opinion, what was important was being "in the zeitgeist", adding Netflix will "ramp up" future information on viewing figures.