We're just three months into 2013 and it hasn't been a great year for Apple (AAPL 0.52%). The company's stock is down 39% from an all-time high back in September and IDC just released numbers this week predicting that Android tablets will outpace iPad shipments this year. But how far has Apple's tablet market share actually fallen and what does it mean for investors?

How far Apple has fallen
When the iPad was first introduced in 2010, the device practically created the tablet market that now seems so commonplace. A mere three years ago, Apple's new device dominated global tablet shipments. But over the past few years, its grip on the market has begun to lose ground, despite strong sales.


Source: IDC.

Apple's tablet shipment market share is expected to be overtaken by Android devices later this year The chart below shows Apple and Android's market share last year, and this year's estimates.

Source: The New York Times.

Judging purely by Apple's downward trend in shipment market share, and Android's upward movement, Apple investors shouldn't be pleased with these numbers. But is it all that bad?

Still the top-selling dog
Apple investors clearly don't want to see the company losing the global shipments game, but there's another set of numbers to consider -- and they're pretty important. When it comes to shipments compared to other manufacturers, Apple still reigns supreme. Take a gander at these tablet shipment numbers for the top five competitors in Q4 2011 and 2012.

VendorQ4 2011 Shipments
(millions)
Q4 2012 Shipments
(millions)
1. Apple 15.5 22.9
2. Samsung 2.2 7.9
3. Amazon.com  4.7 6.0
4. Asus 0.6 3.1
5. Barnes & Noble  1.4 1.0
Others 5.5 11.6

Source: IDC.

In Q4 2011 the company shipped over 15 million iPads and then increased that number by more than 48% year over year. To be fair, Samsung's tablet shipments skyrocketed by 263%, but the company only sold 2 million tablets in Q4 2011, so its rapid percentage growth is in relation to its previously low shipment numbers. When we take these shipment numbers and stack them up against each other, we see how Apple fares against its biggest competitors.

Source: IDC.

Apple's tablet shipment numbers outpace No. 2 Samsung by almost 290%. That's a pretty hefty lead, considering Apple's price point, even with the iPad Mini, is aimed toward the higher-end market, and Samsung's tablets run the gamut of prices.

A look ahead
Apple's competition shouldn't be undersold, but the company does still command a lead in global tablet shipments. With the smaller tablet market expected to take off this year, Apple launched its iPad Mini at the right time and can expect to keep tablet sales strong with the smaller iteration. Investors should keep an eye on Apple's actual tablet sales over each quarter to track how well it's doing against Samsung and other competitors. Samsung is a formidable opponent in both tablets and smartphones, and Apple can't rely on previous sales to maintain its lead.