It's called "positional scarcity." Most fantasy players have heard this term thrown around at the draft table, and many fully incorporate a drafting strategy that includes the concept. However, in my humble opinion, most proponents of this strategy don't fully understand it, nor do they use it properly. Hopefully, after reading this article, that will no longer be the case.

So what is positional scarcity? Well, in most leagues, when you draft a fantasy baseball team, you can't simply select whatever players you want. There are roster and lineup restrictions imposed on your team. You are required to have a certain number of catchers, a certain number of first basemen, a certain number of pitchers, so on and so forth. As a result, most owners will utilize a concept known as "tiering," where they will rank the players who qualify at each position independently of each other, and make a note of where there appears to be a huge drop-off in talent.

Advocates of this theory would say that when it's your turn to draft, it makes far more sense to draft one of a small handful of equally grouped shortstops at the highest tier instead of one of the 15 or so equally ranked remaining outfielders. Why? Well, there's far less of a chance that one of those shortstops will still be around when your next pick arrives, while there's sure to be a viable outfielder or two of equal value still sitting there for you to snatch up.

In other words, the lack of depth at shortstop makes it far more important to grab one of the top performers at that position, lest you be burned by the scarcity that exists there later. Take a look at the following table, which shows the 2008 stats of Hanley Ramirez and Grady Sizemore, each likely to be considered in the top three at his respective position, and Miguel Tejada and Bobby Abreu, each likely to be in the mix around spots 10-12 at shortstop and outfield, respectively.

You can clearly see that there's not a whole lot of difference between Ramirez and Sizemore. However, because of the huge statistical hit you'd take by passing on Ramirez and waiting to pick up Miguel Tejada, you can't select Sizemore here. The combination of Ramirez/Abreu will outperform the Sizemore/Tejada tandem in each and every statistical category. That's the rationale for factoring positional scarcity into the equation when drafting, and it makes an awful lot of intuitive sense. The problem, though, isn't in the theory, but in its application. To explain what I mean, I give you: The Curious Case of Russell Martin.

How should we determine if there is indeed positional scarcity at a particular position? Let's take a look at catchers. The most logical course of action would seem to be to line up all the catchers in the league, and compare their stats. Once we've done that, we can rank them accordingly, and see where we expect a huge drop-off in output to occur. When we do embark on that task, the player who jumps out at us is clearly going to be Russell Martin. His 18 stolen bases at the catcher position shine a huge spotlight on the Dodgers' backstop. In fact, if you totaled up the steals of all of the 108 players who donned the tools of ignorance last season, you'd stop counting at 81. In other words, Martin had 22 percent of all catcher stolen bases. In fact, his share of all catcher stats is pretty impressive in all categories. Take a look:

That last line is mind-boggling. If Martin had the same percentage of all outfielder stats as he did as a catcher, he'd be the greatest player of all time, with 57 home runs, 355 steals and 245 RBIs. In fact, after taking each and every player in the major leagues and ranking their 2008 stats using a positionally weighted scale which I'm calling PSR (Positional Scarcity Rating), we find that Russell Martin is far and away the most valuable player in the league.

But here's where logic has let us down. We were comparing Martin's stats to other catchers. While that might make sense intuitively, it's completely the wrong way to analyze the data. Why? Unless you play in a league where you get points for winning each individual position, Martin's stats aren't going to be compared to other catchers exclusively. They're going to be thrown into the same pot as every other player in your lineup. So while his 18 steals are nice to have from a catcher, they're no more valuable than Denard Span's 18 steals.

So, even though we do want to compare Martin's stats to other catchers exclusively in order to rank the position, we need to weight the value of each stat as it compares to the league as a whole. He doesn't have 22 percent of all steals. He has only 0.6 percent of all steals -- which is still a greater piece of the pie than any other catcher, but far less of a difference-maker in the comparison process. In fact, when we look at the top 10 catchers evaluated in this fashion, we get a far different result.

So, as you can see, Martin is actually only the third-best catcher, and not too far ahead of Geovany Soto. Certainly there is still a huge drop-off once you hit catcher No. 7 on our list, and there is clear evidence that positional scarcity does exist for catchers. However, by evaluating talent in this way, there's no longer an urgent need to grab Martin at all costs as we might have thought if we had simply thrown his stats under a catchers-only microscope.

This is where you can gain a huge advantage over your opposition, since many of them likely will make the very understandable mistake of comparing apples to apples. By being counterintuitive in your analysis, you can actually uncover hidden gems who will be way undervalued by position-exclusive statistical study, as well as players who are sure to be overrated and selected far too early by your competitors.

Here's a list, position by position, of potential sleepers and busts based on the expected improper positional scarcity analysis of most fantasy players:

So, what's the moral of the story? If you're going to use positional scarcity, you need to look not only at each position individually, but also as it relates to the whole. If you fail to incorporate both of these snapshots into your complete world view, your fantasy team will surely find itself moving backward through the standings as time marches on.

*AJ Mass is a fantasy football, baseball and college basketball analyst for ESPN.com. You can e-mail him here.*