As members of the world wide baseball community, we’ve often discussed and read about the ever-growing changes in the level of play between the American League and the National League. One league has the designated hitter, the other does not, so naturally the two leagues will differ to some extent in even the park and defense adjusted numbers for pitchers.

So when John Dewan of ACTA Sports and Baseball Info Solutions, who give us the Bill James Handbook every year, sent out his Stat of the Week last month, I balked.

The title of the stat is “Is there an Adjustment Period for Players When They Change Leagues?”

The data to back up the claim that “no, players do not typically go through an adjustment period when changing leagues,” Dewan uses win shares to compare the last two years of the 23 players that switched leagues last season.

Dewan found that 13 of the 23 players had 2007 win shares total within two win shares of their 2006 season, and that five players showed a decline and five players showed an improvement.

Sounds remarkable until you look deeper.

The five players that improved by three or more win shares are: Jose Vidro, Ted Lilly, Alan Embree, Aubrey Huff and Kenny Lofton.

The five that declined by three or more are: Mark Loretta, Danys Baez, Roger Clemens, J.D. Drew, Barry Zito.

Of the five that improved, two went from the AL to the NL and three came from the NL to the AL, which, on the surface, seems like a little piece of evidence that maybe the two leagues aren’t all that different.

But looking at it further, that fact cannot be made more clear, thanks to Dewan’s study.

Vidro went from 12 win shares to 16 win shares, not a tremendous difference, suggesting that maybe Dewan should have upped the “change” value. But my point is this on Vidro - he was healthy in 2007, and was not in 2006. That makes an enormous difference regardless of the league.

Lilly improved four win shares as well, going from the AL to the NL. Again, not a huge difference, but he was healthy both years and still showed a four WS increase.

Huff wasn’t perfectly healthy in either season and still showed an improvement of three win shares in the NL versus his AL total in ‘06.

Kenny Lofton is the only of the five that was healthy both seasons and improved by more than two win shares in the AL over his previous totals in the senior circuit. But again, three win shares is fairly marginal - it equals one overall win.

Pretty solid evidence so far that the AL is indeed the better league, but, wait, there’s more.

Of the five that declined, only Loretta and Zito showed a decline of three shares or more after moving from the AL to the NL, and Loretta, who lost five win shares between the two seasons, spent time on the DL, played injured for other portions of the season and is in a decline age at 36 years old.

He was very likely to show the same decline no matter the league in which he played, and one could argue that he’d have taken a much more severe step back in production had he remained in the AL where the pitching is far superior.

Zito was just downright mediocre/awful, and I won’t even begin to speak of his decline from 17 WS to eight after stepping into the worse of the two leagues.

But Baez went from six win shares to one, and wasn’t very healthy in either season. Drew appeared healthy in both seasons and dropped from 19 to 12, and Clemens sank from 11 to five, a rather enormous drop for a pitcher.

Clemens’ drop can be attributed somewhat to natural decline as well, same as Loretta, but if we take a look at those 13 that remained about the same, five of them came to the AL in ‘07 but ALL OF THEM had significant prior experience in the better league, and only Miguel Batista and Andy Pettitte, who has admitted publicly that his shoulder was “much more sound from beginning to end” in 2007, were older than 35 when the season ended and did not spend time on the DL - suggesting strongly that they played injured for at least part of the 2006 season.

You can also make a rather large case that Pettitte benefited greatly from the move out of the Juice Box in Houston and into the pitcher-friendly confines in the Bronx.

Dewan is correct in claiming that, based on the 2006-2007 crop of 23 players and their win shares totals, their isn’t necessarily an adjustment period when changing leagues, but my contention goes beyond the simple change of leagues and believe the better, and much more valuable and appropriate question, is clearly whether one league is superior to the other, and by how much. Several of these 23 players make that case soundly in favor the of American League.

It’s the reason why so many scouts are giving two separate projections for free-agent pitchers right now. One scout recently told me that even though Carlos Silva and Hiroki Kuroda are low-4th or No. 5 starters in the AL, they might be able to slide in and put up low-3, high-4 performances in the National League.

The same scout strongly opined that if Alex Rodriguez signed with the Chicago Cubs or Los Angeles Dodgers and remained there for the duration of his career, he’d likely hit anywhere from 50-75 more home runs than he would have had he remained in the AL where he has spent the first 11 years of his career.

Yeah, 50-75 more in seven seasons. That’s as many as eight more per season, which is probably the Wrigley side of things while the 50 better represents Dodgers Stadium’s increase. But that’s an amazing, although conceivable difference.

Now, you can argue those numbers in either direction, sure, but there’s a clear difference in the two leagues, and it’s pretty significant and seems to be getting worse every year.

Buyer beware of the NL’s fourth starters and six and seven-hole hitters. They might just be middle relievers and bench bats in the best baseball league in the world - the American League.

Memo to the Mariners and GM Bill Bavasi: Stop signing and trading for league average arms from a league whose talent level is far below the standard of the league in which your team is playing.

You wouldn’t place last year’s West Tennesse Diamond Jaxx roster into the NL East and expect them to win, would you?

Didn’t think so.

Or would you?