Re: Freight car distribution

Walter M. Clark

--- In STMFC@..., "Bruce Smith" <smithbf@...> wrote:


I grow weary of this. No one has answered Tony's challenge to provide
evidence that supports a "regional bias in boxcars" position. It seems
that any evidence that does not support this position is dismissed as
"absurd" or "biased" and opinion and hyperbole are used in lieu of data.
Many of the arguments that have been used about statistics are not based
in a sound understanding of the field. For example, deviations from the
mean are EXPECTED and do not invalidate the mean. Certainly,
modeling the
deviations would be.... deviant!

What I find truly remarkable is the wealth of DIFFERENT types of
data that
seem to support the national fleet as a starting place for a model
representation. The Charles data is flawed at best, yet it supports the
model. Wheel reports from different locations support the model...

-It ISN'T about individual trains (How often do we need to say this?)
-Individual trains may have very specific make-ups that vary
from the national averages.
-It is about a "fleet"
-That fleet will then fluctuate on the layout of the owner, providing
deviations from the mean... and modeling those deviations that almost
certainly occur in real life.
-It is a STARTING place - I have yet to hear anyone offer a different
starting place based on data other than their own opinion, and frankly,
I'd rather take my chances with the data ;^)
-The model DOES NOT preclude the use of oddballs, but it does INFORM the
modeler that these are oddballs.

Over and out

Bruce Smith
Auburn, AL
Bruce, and all,

What we have is the problem that always occurs when using statistics.
Most people won't accept that a relatively small sample size can
forecast much larger populations with extreme accuracy. Just listen
to the arguments after a national poll is released, where they polled
only a few thousand people and used that data to project within just a
few percentage points of error what the entire Nation's population thinks.

Tim's and Dave's analysis is for an entire year. Not every train, and
not every train in a single month. Neither Tim nor anyone else who
accept Tim's and Dave's calculations are claiming that. It is the
total of all box cars over an entire year. This can (not must, we all
can do what we darn well please on our own model railroads) help me
decide which box car kits, and in what quantities, I need to
reasonably represent the possible activity in my month of November
1941 on my mythical short line that connects to the Southern Pacific
in northern California.

I had a professor in Graduate School who, in the Statistics class,
always brought a cloth drawstring bag with 100 red and 100 black poker
chips to class. No matter what he was teaching, and no matter how big
or how small the numbers he was working with, a handful of chips from
that bag was ALWAYS extremely close to what the calculations said.
And grabbing 10 separate handfuls (counted and replaced in the bag
between grabs) was ALWAYS RIGHT ON! This can be shown in any group of
30 people. Even though there are a total of 366 possible birth dates,
any somewhat random group of 30 people WILL ALMOST ALWAYS have two
with the same birth date.

Intuitively it doesn't make sense, and that's what the naysayers are
arguing. Yes, there are exceptions, and situations that don't match
the calculations, but those exceptions and outlying situations are
smoothed out over time.

Between Tim's and Dave's analysis, and Larry's Excel spreadsheet,
along with a close-to-my-modeling-period ORER I can determine how many
box cars from what railroads I need to plan for, then adjust that as
necessary based on what kits are available to me.

Is it perfect, and can I generate a single freight train that
perfectly matches a single freight train from Fraley? No, but there
is no way to come up with anything more accurate. Perfect? No, but
better than the rest.

Time stopped in November 1941
Walter M. Clark
Pullman, Washington, USA

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