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Vernon Wells is congratulated by his Müllerian mimic. (AP Photo/The Canadian Press,Frank Gunn)

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As we all know, the Chicago White Sox snatched Alex Rios up from waivers earlier this week.  How has a player who was rumored to be involved in a trade straight-up for Tim Lincecum (or at least Matt Cain) fallen so far and so quickly?  Well, Rios is having his worst season (currently at 1.1 WAR) since he was just 24 years old back in 2005.  The Jays signed him to a long-term deal early in the 2008 season and his batting numbers seemed to fall off immediately. 

After hitting 41 homeruns in 1209 plate appearances in 2006 and 2007, Rios has hit just 29 in 1166 over the last two seasons.  In addition to his decrease in power (ISO-P has fallen each season since 2006), he's had trouble getting on base (particularly this season, when he is OBPing just .317).  After posting wOBAs of .365 and .368 in 2006 and 2007, Rios lost a bit last year (.350) and has fallen even farther so far this season (.329).  He is hitting more grounders than he did in '06 and '07 and fewer line-drives, while also popping more balls up.  His HR/flyball rate this year (9.5%) has actually rebounded some from 2008 (7.4%), but it is not quite where it was back when he was really productive at the plate (11% in '06 and 10% in '07).  While all these statistics are essentially telling us the same thing -- that Rios's offensive production has considerably regressed -- it is useful to look at them all, because the more that they agree, the more likely they are to be representative of what is actually happening.

Now, while Rios's offensive value took a huge hit after signing his contract, his defense more than made up for it -- at least last season.  According to UZR, Rios was 23.9 runs above average in the field last season, worth about two wins above the average player after accounting for playing mostly rightfield.  In previous seasons (outside of an exceptional 2004), Rios had been worth closer to 10 runs over the average player (still great, but not otherworldly), and the extra 15 or so runs (he played more CF last season that ever before) more than accounted for his dropoff at the plate.  According to fangraphs, Rios finished the season as a 5.5 Wins Above Replacement player.

To put this into perspective, Dustin Pedroia was worth 6.6 Wins in his MVP season last year.  This season has been an entirely different animal, as Rios's fielding has fallen off sharply -- UZR sees him as merely an average rightfielder -- which, when combined with his dramatic decline at the plate, renders him merely a 1.1 Win player.  Truth be told, Rios is probably somewhere in between, but I have a hard time believing that he won't be a better player going forward than he's been this year (at least for most of his contract).

So why do people think Rios is so bad?  Well, this is a bit of a digression, but biologists have a term called mimicry that can be used to describe the similarity in coloration and appearance between species of different degrees of palatability.  Two common types of mimicry are Batesian, in which one species has an high degree of toxicity and the other is non-toxic, and Müllerian, in which both species are toxic, but to different degrees.  While the Batesian mimic provides no value to the toxic species, the Müllerian mimic actually reinforces non-consumptive behaviour in predators for both species.  Basically, if you eat something green that makes you sick, you'll be less likely to eat something green again (Batesian mimic benefits).  And if you eat two things that are green and both make you sick, you're even less likely to eat something else green (both species benefit).

I argue that Alex Rios is merely a Müllerian mimic of Vernon Wells, who is paid more and has obviously experienced an even more drastic decline than Rios (both at the plate and in the field).  It is easy to associate two well-paid outfielders with one another, but Rios and Wells are not the same player.  We may have a bad taste in our mouths from Vernon Wells, but Alex Rios is actually pretty palatable.