On 16 Jul 2001 09:31:08 -0700, [EMAIL PROTECTED] (dennis roberts) wrote:
[ snip, RTTM is about 'relative' values ... ]
>
> the issue that has to be raised with respect to the baseball example is ...
> are the two halves PARALLEL HALVES? ... like, parallel tests given at
> essentially the same time? well, no, they are not. for parallel tests ...
Yes, I thought it was sort of silly for anyone to raise that question
concerning seasons in team-sports, because sports give such a fine
example of parallel halves: means are the same, variances are
the same. If you are looking at "team wins", those are forced to be
50%.
Individual sports (track) are different, in one sense, because the
season of HS or college meets has a progression of Personal Bests.
But 'margin of victory' is not bigger at the start/ end of the
season.
> if i give form A now and ... and hour later ... form B ... then there is no
> reason to expect the distributions of A and B to be much different ... nor,
> the individual examinees to earn much different scores on form A and form B
>
> this is NOT the case in baseball ... or any sport where there is some
> arbitrary division of 1/2 of the season versus the other half of the season ...
>
It is not a bad *idea* to consider. But it does seem much more
obscure and unlikely than the "hot hand" in basketball. And the
"hot hand" has remained invisible to statistical analysis, in several
attempts.
> these are NOT like parallel tests given to the same examinees ... because
> of many factors ...
>
> 1. weather is different in second 1/2 than first 1/2
> 2. players get injured differentially across the halves ... may not be in
> first half but is in the second half (or vice versa)
> 3. the TEAMS you play may not balance out during the second half the same
> way they did in the first half (better competition or worse competition)
> [ snip, rest]
Okay, if Bonds breaks his arm, he will hit *far* fewer HRs in the
second half. Injury creates a *little* extra variability, by person,
across seasons, especially in 'totals'.
But, so far as I have heard, the league MEANS stay the same.
The SDs are the same. There is no preference, that I have ever
heard, for records to be set by half-season, early or late, team
or individual. My guess is that association between "talent"
and "winning" (or hitting, or pitching, etc.) remains the same.
There might be multiple causes. However, in Major League
Baseball, the outcomes are averaged over hundreds of players,
and hundreds of games. How good is the parallelism? - I think
I should expect more discrepancies in the "parallelism" of
professionally developed psych-tests. For many purposes.
--
Rich Ulrich, [EMAIL PROTECTED]
http://www.pitt.edu/~wpilib/index.html
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