There had been talk yesterday that the Mariners were one of the teams trying to land catcher Ryan Doumit. Instead, he wound up on a one-year, $3 million deal with the Twins.

Not a huge loss for the Mariners. And don't let the numbers fool you. As good as some of Doumit's stats looked last year, he has essentially become a part-time player and that's pretty much what he would have been in Seattle.

A part-time catcher to spell Miguel Olivo, but primarily another first base/DH type of bat off the bench or to rest certain guys.

Now, there's nothing wrong with the Mariners going after these types of role players to round out their bench. But at $3 million, that would have been pretty steep for a guy who looks more like a rich man's Chris Gimenez than a poor man's Prince Fielder (the 1B/DH part, not the catching, clearly).

In baseball, it's important to make the distinction between part-time players and full-time guys who can go the distance. We saw that this season with Adam Kennedy, who put up great early numbers, only to have his aging body run out of steam as he was thrust into a full-time role. It's why the Mariners never dared use him in an outfield role where he'd have to sprint after balls, despite the fact he'd played some games there before.

With part-time guys, both young and older, the numbers tend to drift downwards as playing time increases. Was the story of Willie Bloomquist's career in Seattle. Been the story of many part-time careers.

So, you can't just do the easy thing and look at Doumit's slash line and say, wow, he hit .303/.353/.477 over 236 plate appearances! Maybe he can keep that up over 600 plate appearances and our hitting woes are solved!

No, it doesn't work that way. Once in a blue moon, maybe.

But when you look at Doumit's 2010 season, when he had 456 plate appearances, his slash line was just .251/.331/.406, that's what you'd be more likely to get as his plate appearances increase. In fact, Doumit has never had more than 465 plate appearances in any season and that was back in 2008.

Major league teams are well aware of these things and that's why they tend to categorize players as full-timers and part-timers. Sometimes, they're wrong. Most often, they aren't and these things are reflected in free agent salaries.

There's a reason guys like Albert Pujols, Fielder and other big bats will be offered several times more than a guy like Doumit, even though their stats may not be that many times better by proportion.

It's because you can't try to directly measure the production of a part-timer versus that of a full-timer. Sounds easy enough to understand, but it's a mistake many fans often make without even realizing it.

If you were going to compare the cost of bringing in Pujols, for example, with that of Doumit, you can't just subtract the difference between the two guys and assign a dollar value to what each guy's numbers cost.

Because one guy is producing the numbers over an entire season, day in and day out. While the other is in a part-time role and you know his numbers will likely tumble by a lot if he played as many games.

When you pay for a guy like Pujols or Fielder, you are paying for the consistency of their full-time production more than anything.

Photo Credit: AP

You can try to estimate what the dropoff would be if a part-timer expanded to a full-time role. Try to take averages of all other such players when their roles expanded. But it varies so much from guy to guy. Depends on age, home playing surface, the position they're at. We can try to narrow it down some, but it amounts largely to guesswork and not very certain at that. There is no real formula to predicting that future, just a whole lot of finger-crossing and extra care taken.

About the only certainty is, you start playing part-timers too much, you will often be left disappointed.

A nice exception to this rule for the Mariners was Russell Branyan in 2009, who performed quite well in his first full-time assignment...until, that is, he got hurt. So, a skeptic would say he didn't last as a full-timer, even though he had great stats until August. Branyan has not succeeded in a full-time role since.

Anyhow, that's why there's such a cost difference between part-timers and full-timers.

And while the simple solution would seem to be "Hey, just get a bunch of part-timers and share their plate appearances" this strategy is one that teams try to avoid. We've all heard of great platoon stories and such. The Angels were known for rotating guys around the diamond and getting results. But it doesn't always work out so well. We tend to ignore the stories of platoons that flop, largely because they don't last long enough to be remembered. Most teams would prefer to have guys they know they can count on day in and day out taking the field rather than shuffling guys around depending on what day of the week it is.

So, again, this Doumit thing is part of the small potatoes portion of this Mariners off-season. Don't get me wrong, he would have made a decent bench addition. But not for that $3 million price.

This team has to focus its big financial resources on full-timers.

That's why Erik Bedard won't be rejoining the Mariners. Bedard is known as a guy who puts up very good numbers when healthy. But he can't finish. Keeps getting hurt.

The Mariners made it clear at season's end they want more players who can finish. They've made it abundantly clear to shortstop Brendan Ryan, who endured a second half injury and fade.

And guys who can finish are the start of building a championship team. Numbers are just that. Numbers. You can throw them around, try to average out the cost per hit or run generated and stuff, but that's a fool's errand. It doesn't tell you nearly as much as you'd think and that's why teams don't operate this way. It's how often and consistently you can repeat those numbers that largely determines your overall value and how much you'll be paid as a free agent. And if you can consistently put those numbers up over 150 games per season, you will be viewed as a likely bet to continue to do so (age and injuries factored in, of course).

In this case, Doumit brought limited, part-time value to a Mariners team with much bigger priorities for off-season improvement. This team has much bigger fish to fry and can't afford to spend too much money for part-time production, even if the numbers did look good over the short haul.

Because you can't compare the numbers of a part-timer versus a full-timer. They are two very different things. And believe me, the Mariners understand this quite well.