You know eBay (NASDAQ:EBAY) is the online auction king. There's no real competition, but with its stock trading about 25% off of its 52-week highs, you might wonder whether the price represents a good value.

That's the traditional way some people look at and value stocks. But maybe we need a fresh perspective. Instead of wondering whether eBay is a good value, maybe we need to see whether it's even possible for it to achieve its business goals to support it at this level. We know auctions and listings drive eBay's value, but have we thought about whether eBay can sustain this number of auctions and listings?

Chances are, most investors haven't, but the folks at TransparentValue have. Instead of looking at the price, they're looking at what eBay does to see if it justifies its valuation. To do so, TransparentValue digs in to see just how many units would need to be sold or shipped to determine the revenue needed to justify the stock's valuation. They call it a company's required business performance (RBP), and the probability of management being able to achieve the result to support the current stock price is recorded in a percentage.

How much wood can a woodchuck chuck?
Whether it's online auctions and listings for eBay, iPods for Apple, or shipments for FedEx (NYSE:FDX), every business has a unit or metric that drives its numbers. The higher the company's RBP probability, the more likely it is that management can deliver the performance, so a company's value -- its stock price -- is directly linked to management's ability to drive revenue.

What's your risk profile?
In eBay's case, it has roughly 2.4 billion listings on its site over the past 12 months. To justify its current price of around $31 a share, TransparentValue calculates that eBay will need to gain 2.9 billion listings for the year in three years. What's the probability that eBay will achieve this? According to TransparentValue, 100%!

How much risk are you willing to accept? It's certainly a subjective question based on personal preferences and tolerances. Motley Fool Stock Advisor recommendation FedEx has a slight 5% chance that it won't be able to make enough ground, express, and freight deliveries. Because that ranks first out of four delivery services (and second out of 22 industrial transportation companies), it might be a good fit for a conservative investor.

What the FedEx numbers seem to quantify is the original rationalization for its selection by Stock Advisor: It's a pure play on globalization. Moving packages worldwide is a complex business, and FedEx has been reinvesting in its worldwide logistics network of planes, trucks, and hubs. Conversely, with a 50-50 shot at making good on its RBP numbers, United Parcel Service (NYSE:UPS) is a much riskier investment, though its recent deal with DHL might help lower the risk profile. That's bad news for Air Transport Services (NASDAQ:ATSG), which used to rely on DHL contracts for about 74% of its revenue and 69% of its pre-tax profits.

A world of stocks
Of course, there are no guarantees that even eBay, with a 100% RBP probability, will actually make those numbers, but it's an educated and back-tested guess. I wouldn't make an investment decision based on any one data point, but the TransparentValue site gives investors another tool.

Investors who are looking for winning stock ideas but don't have the time to take a close look at the numbers can check out Stock Advisor, which over the past six years is beating the market by an average of 43 percentage points.