Like Apple (AAPL) - Get Apple Inc. (AAPL) Report , Facebook (FB) - Get Facebook, Inc. Class A Report and some other tech companies, Twitter (TWTR) - Get Twitter, Inc. Report is changing up what metrics it chooses to report -- and it's not hard to understand why.

In its Q4 shareholder letter, the microblogging platform announced that it will stop sharing its monthly active user (MAU) count after Q1. Instead, Twitter will share its monetizable daily active users (mDAUs), which it defines as "Twitter users who logged in or were otherwise authenticated and accessed Twitter on any given day through or Twitter applications that are able to show ads."

Prior to its Q4 report, Twitter wasn't disclosing a DAU count of any kind, instead only sharing its mDAU growth rate. It now states that mDAUs totaled 126 million in Q4, up by 2 million sequentially and 11 million (9%) annually.

On the flip side, MAUs fell by 5 million sequentially and 9 million (3%) annually to 321 million. That's worse than the 4 million-user annual MAU drop recorded for Q3. In North America, which still produces over half of Twitter's ad revenue, MAUs fell by 2 million annually to 66 million.

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MAU worries appear to be part of the reason Twitter's shares fell over 9% post-earnings on Thursday. Also weighing: Though the company beat Q4 estimates, it guided for Q1 revenue of $715 million to $775 million (below a $763.5 million consensus at a $745 million midpoint) and forecast its GAAP and cash operating expenses will rise about 20% in 2019, after growing 8% and 17%, respectively, in 2018.

Twitter's monthly active users continue declining. Source: Twitter.

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Facebook, it should be noted, reported last week that MAUs and DAUs for its core service and Messenger each rose 9% annually in Q4, with MAUs totaling 2.32 billion and DAUs 1.52 billion. It also managed to grow its user counts sequentially and annually in North America and Europe, in spite of recent usage pressures for the core service in those markets.

To be fair, Facebook also signaled on its earnings call that it will phase out sharing user metrics that only cover core Facebook and Messenger in favor of metrics that cover its entire "family" of services, including Instagram (1 billion-plus MAUs) and WhatsApp (1.5 billion-plus MAUs). The company said it estimates 2.7 billion people use at least one of its four main services on a monthly basis, and that over 2 billion do so daily.

Regardless of how its metrics are sliced, Facebook's MAU growth is holding up better than Twitter's in spite of the deluge of negative publicity and government scrutiny it has received over the last 12 months. Moreover, while Twitter's DAU growth is faring better, the mDAU figures it just reported are a little underwhelming.

Back in mid-2017, Twitter was estimated to have 140 million total DAUs as of Q2 2016, and 157 million as of Q2 2017; now, it reports having 126 million monetizable DAUs. In addition, Twitter reports having just 27 million mDAUs in the U.S. in Q4 (up by 2 million annually), and 99 million elsewhere. For comparison, Facebook and Snap Inc.  (SNAP) - Get Snap, Inc. Class A Report reported having 186 million and 79 million North American DAUs in Q4, respectively.

Twitter's "monetizable daily active users" are growing moderately.

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The glass-half-full way of looking at this is that Twitter still has a lot of headroom to grow daily usage in the U.S., which remains by far the world's biggest digital advertising market. The glass-half-empty view is that Twitter -- after many years of talking up the expected impact of service improvements on user growth -- is still only modestly growing daily usage, and that its U.S. mDAU count makes it a niche platform in the eyes of U.S. advertisers relative to Facebook proper and Instagram.

To reiterate what I've argued on a few prior occasions, Twitter -- in spite of the considerable value it provides to its die-hard fans as a news, entertainment and opinion platform -- still hasn't figured out how to grow a larger base of social media users the way that Facebook and Instagram have. While one can blame a number of potential culprits for this -- from the lack of engagement that many regular Twitter users see for the tweets they share, to the abuse and vitriol that can still be found on some corners of Twitter, to the text-heavy nature of the service -- the company's user metrics make the problem quite clear.

And this holds true for both the age-old user metric that Twitter plans to stop sharing, and the new, slightly better-looking metric it will be sharing from now.