In the hype-filled world of the tech sector, there are lies, damned lies, and market share statistics.

No, the market share numbers themselves are mostly legit: Industry research firms such as Gartner, IDC, and Strategy Analytics put a lot of effort into estimating unit shipments of PCs, cell phones, servers, and other kinds of tech hardware from leading manufacturers with a reasonable amount of accuracy. But those numbers often bear little relationship to a manufacturer's share of an industry's revenues, never mind its profits.

Nokia's strong market share ...
There's probably no better example of how deceptive industry market share can be when it comes to judging a company's financial strength than Nokia (NYSE: NOK). If your opinion about the strength of Nokia's mobile phone business in recent years was based only on market share numbers, which are typically based on unit shipments, you'd probably think Nokia has been doing a pretty good job of weathering the competitive challenge posed by Apple's (Nasdaq: AAPL) iPhone, Research In Motion's (Nasdaq: RIMM) BlackBerrys, and a variety of phone manufacturers relying on Google's (Nasdaq: GOOG) Android. For the first quarter of 2010, IDC estimated that Nokia's share of global mobile phone shipments stood at a healthy 36.6%. That's only slightly below the 38.2% share IDC gave to Nokia for the whole of 2007, and actually above the 34.2% assigned to the company for 2006.

Meanwhile, though Nokia's share of the smartphone segment of the mobile phone market took a hit in 2008 -- a year in which iPhone and BlackBerry sales really took off -- market share numbers suggested that the company had been holding its own in the following quarters. Research firm Canalys estimated that Nokia's share of global smartphone unit shipments in Q1 2010 amounted to 38.8%; this was roughly even with the 38.9% share Canalys estimated for Nokia for Q3 2008, and translated into 38% smartphone unit shipment growth for the company during this time frame.

... And slumping profits
But alas, those healthy market share numbers completely sidestep the fact that Nokia's mobile phone revenues in recent years didn't come close to keeping up with its unit shipments. From the first quarter of 2007 to the first quarter of 2010, the average selling price (ASP) for Nokia's phones fell more than 30%, from 89 euros to 62 euros, as its sales became increasingly slanted toward cheaper models targeting developing nations. And though Nokia has only recently begun breaking out its smartphone ASP, we know that, just between first quarter 2009 and 2010, this number fell by more than 18% to 155 euros -- less than half of the sky-high selling prices reported for the iPhone and high-end Android devices such as the Motorola (NYSE: MOT) Droid X and HTC EVO 4G.

Thanks to this massive drop in ASPs, revenues for Nokia's "Devices & Services" division plummeted by more than 28% from first quarter 2008 to 2010. And in an industry where a disproportionate share of gross profits come from sales of high-end smartphones and other costly devices, Nokia's ASP drop produced a stunning 57% fall in the division's operating profit during this time period.

From that angle, it becomes obvious that Nokia sure wasn't holding its ground in the mobile phone market in recent years -- and especially not in the pivotal smartphone segment. The performance of Nokia's stock price of late -- its shares are down over 60% during the past 24 months, compared with a drop of less than 10% for the Nasdaq -- show just what a huge mistake it would have been for investors to hold onto Nokia shares because its unit shipment share looked healthy.

Apple the profit-margin king
Just as cell phone market share numbers painted a rosy picture of Nokia's business, they didn't begin to do justice to the enormous profits Apple has raked in from iPhone sales from 2007 onwards. Though Steve Jobs & Co. still haven't joined the ranks of the world's top five phone manufacturers in terms of unit shipments, one recent study estimated that the iPhone's phenomenal ASPs and profit margins translated into Apple possessing 48% of the industry's earnings before interest and taxes (EBIT) during the second quarter of 2010.

Likewise, anyone relying on PC market share data to judge the strength of Apple's Mac business would also be selling the company short (figuratively, if not literally). With Mac sales historically skewed toward high-end computer buyers, Apple's PC ASPs and profit margins have long been well above industry averages. And over the past couple of years, this gap has grown even larger due to the fact that Apple has stayed out of the rapidly growing netbook market, choosing instead to offer the iPad as a netbook alternative.

Thus, while Apple's Mac sales account for little more than 4% of the PC industry's global unit shipments (based on the company's data and IDC), a report from Deutsche Bank estimated that Apple took in 35% of the industry's operating profit in 2009 -- easily outpacing unit shipment leaders Hewlett-Packard (NYSE: HPQ) and Dell (Nasdaq: DELL), along with everyone else.

Of course, the huge returns delivered by Apple's shares in recent years have been ample proof of the company's status as a giant money-maker. But anyone who was judging Apple based on market share data from the likes of Gartner and IDC would have deemed it overhyped and overpriced, all the while deeming Nokia to be a screaming bargain.

That's as good an argument as any for why poring over market share data can be harmful to an investor's financial health -- at least when it's done without maintaining a healthy sense of perspective.

Fool contributor Eric Jhonsa has no position in any of the companies mentioned. Google and Nokia are Motley Fool Inside Value selections. Google is a Motley Fool Rule Breakers pick. Apple is a Motley Fool Stock Advisor recommendation. The Fool owns shares of Google. The Motley Fool has a disclosure policy.