Re: We have the pitching, what about offense?

On Jan 21, 5:58 pm, McDuck <wallyDELETEMEMcD...@xxxxxxxxxxx> wrote:
On Wed, 21 Jan 2009 05:25:08 -0800 (PST), jvampate...@xxxxxxxxx wrote:
On Jan 21, 2:25 am, McDuck <wallyDELETEMEMcD...@xxxxxxxxxxx> wrote:
On Tue, 20 Jan 2009 06:09:23 -0800 (PST), jvampate...@xxxxxxxxx wrote:

So there's no reason whatsoever to suspect that Pedroia will not
continue to hit like he has the past two years.  It's right in line
with what he's *always* done, at every level.  Red Sox fans have very
good reason to be optimistic about Pedroia moving forward.

Be optimistic all you want. You just have offered no basis for it.

You mean aside from the fact that all his data up to this point
suggests that he's doing exactly what he's always done:  be a great
hitter?

Exactly. None of that data, which we all know, suggests that he is
immune from the tendancy of a player to revert to the mean.





I said that the betting side is that he'd revert to the mean. You say
he'd do as well as he has the last two years. You apparently fail to
understand that doing the average of the last two years is exactly
what is meant by "reverting to the mean" (for a guy who has only been
in the majors for two years plus a bad month in 2006).

Reverting to the mean would mean a drop in OPS (for example)  of
around 23 points. That is a fairly small decline, and I predicted a
fairly small decline for that reason. As I noted, there are some
reasons for optimism that Pedroia could beat the odds, so to speak,
and improve. But your numbers provide no basis for that optimism.
Indeed, as noted above, you actually are arguing for my exact position
by implicitly predicting that he's do the average of the past two
years.

First, I said that every level he's ever played at indicates that
Pedroia is doing exactly what he's always done - put up great
numbers.  No reason to think he won't do that again.

Second, I think regressing to the mean is a silly exercise when the
major league sample size is so small.  Year one:  a guy hits 10
homers.  Year two, a guy hits 14 homers.  Regression to the mean
implies he'll hit 12 homers the third year.  But with such a small
sample size there's zero reason to think that an increase from 10 to
14 homers doesn't simply represent normal progression in a player.

You are wrong, of course. But we are not talking about HR and small,
perhaps random stuff. Whether a player hits 10 or 14 HRs in a season
may just be luck.

Oh, so "small" stuff *does* matter. Like small sample size. So we
agree on that in principle, then....now it's just a matter of where we
draw the line in terms of what constitutes a small sample size.

Having an OPS of .800 rather than .750 is not luck,
or at least far less likely to be luck. If you want to make what
amounts to a "luck" argument, you need some statistical tools. I doubt
you know enough stats to ue those tools, so I'll not elaborate here.



It may turn out that you're right - doesn't make the sample size large
enough to be significant for your argument.  Yes, I know you'll say
otherwise, of course.

The bottom line is this:  none of us know what Pedroia will do this
year.  He may get hurt and miss 80 games.  He may put up a .900 ops.
He may "regress to the mean" and put up an average of the past two
seasons.  He may have an awful year and then everyone will say he was
a fluke.  His career trajectory suggests that his numbers should
continue to be outstanding and may even improve (as with a normal
growth progression), and it's not really being an unrealistic optimist
to think so.

The above statement is correct. No stat errors that I can see. We
certainly do not know what he will do. But we do know that there is a
tendancy to revert to the mean, so there is some reason to expect some
small decline (because the mean and 2008 are not THAT different.

But why do you get so argumentative? Why not just admit tht you made a
mistake and dis not understand what "revert to the mean" meant? You
could have avoided all the embarrassing cover up stuff, pretendig you
were "really" right when you said Pedroia was more likely to do as he
has averaged for the past two years than it was that he's regress to
the mean.

<sigh> Here's a quote by an engineer about reverting to the mean:
"As an engineer (well, I got the degree anyway) I've always enjoyed
science and mathematics. One of my favorite expressions - revert to
the mean - has to do with systems or processes that swing outside
expected boundaries. Generally speaking, a series over a long period
of time may experience highs and lows, but usually settles back at the
mean." (from http://workingsmarter.typepad.com/my_weblog/2005/11/revert_to_the_m.html)

Note the "long period of time" and systems that "swing outside
expected boundaries". We don't know that Pedroia's 2008 year was
"outside expected boundaries". You're a lawyer, not a statistician,
and please don't claim any level of expertise here. I'll take the
word of a mathematician and engineer in this area over yours, thanks.

(Also, you apparently do not understand what "sample size" means, not
that it matters much. We are looking at all of Pedroia's ABs in the
majors, not some sample --- stated differently, our sample is 100% of
the cases --- can't get any bigger sample than that.)

LOL. That's a ludicrous argument. Of course our sample size is 100%
of his at-bats, but that doesn't mean it's not a small sample size and
that it "can't get any bigger" than that. Just plain stupid. If he
only had five at-bats in the majors, and we looked at all five, that's
100% of the cases, right? Can't get any bigger sample than that?
It's not the percentage of cases we're looking at, it's the raw number
of cases. Regression to the mean when you're looking at 10 at-bats is
pointless...it really is. And yet that may be 100% of the available
data. Of course you can still do the math and it probably comes out
correct, but the context of this discussion is trying to predict what
Pedroia will do next year. Five years' worth of at-bats is a hell of
a lot bigger sample size than two years and change. You're really,
really reaching here.

John
.

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