Re: Freight car Distribution...help with ICC report


Bruce Smith
 

Jeff Aley says:
Thus, a UP modeler should have PRR as 14.59% of his "foreign" cars (after
accounting for regional bias, etc.).
Mike replied
Again...why? Couldn't more PRR "away" cars than their % of the national
population be found on the B&O and C&O, thus reducing their numbers on the
UP...as far as the report says.
Arrrrgh! I can't take this anymore! Like Mike, I've been trying hard not to jump in, yet again, but... well...

First, Mike, isn't that exactly what Jeff implied, by inserting that business about "after accounting for regional bias" <G>.

Second, "regional bias" is just another name for the old modeler- driven paradigm that the NG hypothesis was meant to refute. It is NOT part of the hypothesis.

Third, statistically speaking, it is possible, but incredibly unlikely that on April 13, 1953, ALL away PRR boxcars were on the UP. Thus any discussion of where any cars were at any given time has to be tempered by the inclusion of TIME and the concept of averaging and the realization that any one instant in time would likely NOT reflect that average. Thus, on AVERAGE, over some period of time (months), one might expect that between 14% and 15% of the foreign boxcars on any given railroad (except the PRR) would be PRR cars (and that these would statistically break down into car classes based on the number of cars in each class). Since Mike models one day in time, that particular day need not represent a precise "snapshot" of the US car fleet, although barring other information, that would be a good place to start. Since I model one month, and not a particular day, then, based on the NG hypothesis, my "fleet" (the cars that will be seen over the course of that month) should represent the national fleet. That DOES NOT mean that each operating session will precisely mimic the national numbers (and certainly NOT each train), because there will be randomness to the car assignments, but, over the course of many operating sessions, a pattern will emerge that will resemble that seen on the real PRR at the time I model and that my operators will get the "feel" that some foreign cars were more common than others.

Regards
Bruce

Bruce F. Smith
Auburn, AL
http://www.vetmed.auburn.edu/index.pl/bruce_f._smith2

"Some days you are the bug, some days you are the windshield."
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