Netflix has come to the rescue of many shows since it got into the streaming business - including, most recently, Fox's Lucifer and the long-gestating adaptation of Locke and Key - but how does the company decide which shows are worthy of staying on its roster? After years of being perceived as a network that was slow to cancel shows even if they weren't generating much buzz (really, we needed two seasons of Flaked?), Netflix has been more willing to swing the axe over the past couple of years, with the cancellations of Sense8, The Get Down, and Everything Sucks sparking outrage - and passionate revival campaigns - amongst loyal fans.

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Retention rate

Every TV Show Canceled in 2018 91 IMAGES

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Variety

The global streaming platform doesn't release traditional ratings or disclose viewership numbers for its projects, so there's been no real way to deduce what goes into Netflix renewal and cancellation decisions - but at the Television Critics Association summer press tour, Netflix's VP of original programming, Cindy Holland, finally shed some light on the company's criteria."The biggest thing that we look at is, are we getting enough viewership to justify the cost of the series?" she revealed. "We also look at other things: how beloved the fan community is, how social a title is. There are lots of other things that we look at that you all can also see out in the world. But we are deliberate and thoughtful, and there are a lot of things that go into the decision."Below, we break down some of the other metrics that Holland mentioned that apparently help Netflix decide whether to save or sink a series.Viewer retention is something you'll be hearing about a lot more frequently as streaming platforms begin to dominate the TV landscape. While it's obviously always been important for linear TV networks that ratings stay consistent throughout a season, traditionally broadcast shows also have the ability to pick up additional viewers through multiple airings, summer reruns, video-on-demand or streaming windows, and home video releases. For shows that only debut on a streaming service rather than premiering somewhere else first, platforms like Netflix, Hulu and Amazon are paying a lot of attention to not just how many people initially watch a show, but how many finish the season.According to Holland, this was what doomed Everything Sucks, which was a critical darling, but apparently couldn't retain its viewership across its freshman season: "I’m really passionate about [Everything Sucks] myself. We take the cancellation decisions as personally as anybody, frankly, because we’ve all worked so hard and invested alongside the creators in the show," she said. "In the case of Everything Sucks, it had a passionate and good audience coming in, but what we were finding is that there were far fewer people than average who were completing the season. And so when we looked at what it would take, how many viewers we would need to be successful with a Season 2, we found that the audience size really just wasn’t there."Holland didn't specify what kind of time period Netflix is looking at for a user to complete every episode, but if you love a show, you probably shouldn't wait too long to finish the season, just in case.Obviously, a show that Netflix produces in-house is more valuable than a show produced by a third-party partner, because the streaming network can then control worldwide distribution rights (and reap all of the profits). While fans have been hoping that Netflix might save Freeform's Shadowhunters the way it rescued Fox's Lucifer, that appears to be a pipe dream because the production studio, Constantin Films, no longer has an output deal with Netflix, which was previously helping Constantin and Freeform finance the show. (Bigger studios, like Warner Bros., the company behind Lucifer, typically pay for a large chunk of a show's production cost and recoup their money by licensing a series to a network, like Fox or Netflix, while also retaining the rights to syndicate it, sell it overseas or release it on home video).According to the Hollywood Reporter, Freeform cancelled Shadowhunters because "Constantin lost its output deal with Netflix, which helped to foot the bill for the pricey project. Without the streaming giant's financial backing, Constantin sought a greater cash infusion from Freeform, which sources say was unable to afford to keep the series running." That doesn't necessarily mean that Netflix couldn't partner with Constantin again to revive Shadowhunters once its final episodes air on Freeform, but perhaps Netflix doesn't think it would be worth splitting the cost with an outside studio if it can't have full ownership, or maybe Shadowhunters' viewership hasn't been high enough on the streaming platform to justify it. (Or perhaps they're just playing hard to get.) Either way, Holland seemed to leave the ball in Constantin's court at TCA."Shadowhunters is a Freeform show, so we don’t control the show. I do know that there are another 12 episodes coming to Netflix in 2019. Beyond that, I couldn’t really say," she said, when asked about revival chances. "It’s a very active fan base. I probably get 100 emails a day — more — personally. And I know that there’s a great fandom for the show."On the other hand, if a network has the kind of global reach (and deep pockets) that Netflix has, a show's popularity in other countries could be enough to save it, regardless of whether Netflix owns it outright or not. Holland implied that Lucifer's international popularity was part of the reason the streaming service wanted to save it: "Lucifer is a fantastic show that has really resonated with audiences in parts of the world where we have licensed it. So we felt it was important for the licensing team to try to help that show continue for our fans."Traditional TV networks have built their success on giving their audiences one particular thing without deviating too much from a reassuring formula: CBS is known for its procedural crime dramas, while The CW has carved out a niche as a home for genre and superhero shows. But Netflix hopes to be all things to all people, so producing a broad swath of content that will appeal to many different viewers is part of the company's mandate, according to Holland."Our job is to provide enough variety so that 130 million members find content they love and come back to us every month and so that we can attract the next 130 million members and beyond," Holland said in her opening TCA remarks. "We’ve been focused on broadening our slate and expanding into new areas while maintaining the high bar we set for ourselves from the very beginning. With more than 300 million potential viewers at any given time coming to the Netflix service, we want to offer a wide variety of high-quality programming. Quality and quantity are not mutually exclusive. We maintain quality as we grow by hiring brilliant talent who are passionate about the stories they want to tell and give them creative space."Sometimes that creative freedom can be a double-edged sword ( and lead to pacing issues ), but for now, plenty of producers still want to crack Netflix's formula and earn a place on the homepage in front of those 300 million potential viewers - and if there's already a secret algorithm for success, Netflix isn't sharing it.

For more on Netflix, get a first look at new supernatural drama The Innocents, check out premiere dates and first look at Jonah Hill and Emma Stone's Maniac and The Chilling Adventures of Sabrina , and find out what new animated comedy Disenchantment has in common with Futurama and Rick and Morty