Re: freight car distribution - rejecting the equal distribution hypothesis.


Mike Brock <brockm@...>
 

We are getting to the point...not unlike discussions about color...where we
are not seeing anything new. So...we are getting to the point where the
thread will need to be terminated. Obviously some members are convinced
regarding the Nelson/Gilbert theory's validity and others are not. Before the thread is terminated...until new data becomes
available, I would appreciate seeing some clarification on a few points.

Tony Thompson writes:

"I personally think Tim's data say very clearly that the
appearance of free-running cars like box cars DID follow,
statistically, not absolutely with mathematical precision (Tim never
said anything like that, so let's drop it now), the proportions in the
national car fleet."

What does that mean? In the 1947 data covering Laramie to Green River, the
theory predicts [ I guess that's a good word ] 28 SP box cars. The actual number was 34...a 20% error. In the 1949 data, the theory predicts 52 SP box cars. The actual number was 136...or an error of 161%. Now...when I have mentioned this before, the answer was...nooo problem. This is statistics. OK...fine. No argument. Suppose that damned UP train with the 36 SP box cars was in Fraley's sample. Now the error would be 230%. What if 5 more such trains showed up? 576%. What if it were 1000%? Or 10000%? When does it become a problem...or are the violating SP numbers just thrown away? If the reply to this is that an error of 161% is OK, why bother with the individual national %? Just take the acceptable SP number of 136 = .01 (Y) (1325 box cars), Y = 10.2% and use it for all RR's? After all, SP's national % of 3.6% is fairly representative of all RR's except for PRR and NYC. Just add 5% more for them. I guarantee that the "error" between the actual national % for CGA, Rutland or FEC won't produce a worse error than using the actual SP national % does with the Fraley 1949 data. And, it will be a lot easier to do...don't have to look up anything. Of course, the same thing can be achieved by just acquiring the same number of cars for every RR except PRR and NYC. Get two of each of those. Then do the same thing 3 more times until you have 4 cars of every RR except PRR and NYC which you will have 8 of. I guarantee that will get you in the envelop of statistical success just as much as taking ther national % for each RR.

"The point is that it's the
underlying reality. Anyone who doesn't have better data than Tim's will
just have to get used to it."

As far As I know, Tim's data was the 1947 Fraley and the Southern RR data on a train in Asheville. I gave Tim a copy of my Fraley [ 1949 ]. Did he use any other data of actual car reports?

Mike Brock

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