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Apple's iPhone 6s is doing a good job converting Android users. Image source: Flickr user Karlis Dambrans

For investors, Apple (NASDAQ:AAPL) is somewhat of a paradox. The company continues to be undervalued and underappreciated by the stock market. At this point, the stock trades at a price-to-earnings ratio under 13, while the greater Nasdaq 100 trades at a multiple of 23. This would be understandable if the company was having problems growing its bottom line, but the company grew EPS an amazing 43% on a year-on-year basis last fiscal year.

How did Mr. Market reward Apple during this period? On a one-year basis, company shares are down roughly 1%, while the Nasdaq 100 is up nearly 9%.

What's the reason for this divergence between Apple's amazing operational performance and its sluggish stock price? Investors are worried about its path forward, most notably, future sales of its signature iPhone device, which now accounts for roughly two-thirds of the company's top line after three quarters of 50%-plus year-on-year growth followed by a "slowing" quarter of 36%.

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Source: Apple's quarterly reports. Revenue figures in millions.

On an industry-wide basis, these bears appear to be correct. Both Gartner and IDC have reported a deceleration of smartphone growth in a maturing market. The former's recently released third-quarter smartphone shipment report found the market had cooled to 15.5% year-on-year growth, down from 20.3% in last-year's corresponding quarter.

Earlier this year, IDC marked down its 2015 smartphone shipments figure from 11.3% growth to 10.4%. This is down from the 27.5% recorded last year. That said, research firm Consumer Intelligence Research Partners, or CIRP, brings good news to Apple amid a potential slowing-growth market, showing that more folks are switching to the Apple ecosystem: 26% for the iPhone 6s in its first month vs. 12% last year.

You can still make money in a slowing market
Perhaps one of the biggest fallacies is that a business cannot make money in a maturing market. And that's simply not true. As a matter of fact, maturing markets convey a few benefits.

First, a maturing market discourages new entrants, and secondly, "shakes out" weak[er] competitors (see: the Fire Phone). Of course, in order to continue experiencing strong growth in a maturing market, participants must rely on growing their market share. And that's what it appears Apple is doing, according to CIRP, which says the percentage of iPhone 6s and iPhone 6s Plus buyers who were previously Android users is 26%, a high for the last three iPhone launches. Last year's hugely popular iPhone 6 iteration actually only achieved a 12% switcher rate, and the iPhone 5s had a switcher rate of 23 %. Apple CEO Tim Cook has been quite vocal in his desire to convert Android users, and this data suggests his earlier figure of 30% switcher rate in the fourth fiscal quarter could be accurate.

Bad news for Samsung?
The much-larger switch rate this year over last is noteworthy, and perhaps bad news to Apple's high-end Android competitor Samsung (NASDAQOTH: SSNLF), which two years ago released its most-popular Galaxy model: the S4, which runs on Android and boasted more than 80 million units sold. Many of those users are now coming off-contract, or are looking to upgrade technology. The CIRP data suggests  Apple's doing a good job converting these users.

A word of caution for Apple investors: CIRP's data does not address total sales, merely the composition of iPhone buyers. Although it's good news that Apple appears to be increasing its share of the total pie, as Apple-to-Android switchers appear to occur much less frequently, we're still unsure how big that total pie will be. While I doubt Apple can continue its insane year-on-year growth rate of 50%-plus -- mostly because the comps are tougher now -- it's good for investors to see the company is consolidating market share in a potentially slowing growth market.

Jamal Carnette owns shares of Apple. The Motley Fool owns shares of and recommends Apple. The Motley Fool recommends Gartner. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.