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Regression

Posted on 2011-09-07
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Hi Experts,

Please find attached an excel spreadsheet containing 2 charts and 4 data plots. What form of regression would most accurately model this data? At the moment I have a linear plot selected but it seems to me the data plots have a subtle s shape.
HA-EP-BA.xls
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Question by:DColin
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d-glitch earned 500 total points
ID: 36499409
Those are actaully pretty good fits.

What is the data, and why do think there should be any fit at all?

I do see something in the data that looks vaguely sinusoidal.
You might try a Fourier Transform to see if that's the case.
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by:ozo
ID: 36499425
What relationship makes the most sense for the kind of data you have?

You can produce a fit to random noise and allowing more subtle shapes can produce better fits to random noise, but they would not be any more meaningful.

Asking for an arbitrary model for arbitrary data makes no sense.

You need to start by asking what kind of model makes sense for what the data represents.
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by:DColin
ID: 36499491
Hi d-glitch:,

"You might try a Fourier Transform to see if that's the case."

Can excel do this?
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Author Comment

by:DColin
ID: 36499516
Hi ozo,

The X-axis represents ability, 1 best 20 not best. Y-axis represents earnings.

I have no idea what relationships I am looking for. I was hoping these data plots would tell me what the relationships are.
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by:deighton
ID: 36501389
hi, I too thought the same as Dglitch, that there might be a sine wave in there, but there seems little logical explanation of why that would be, given your explanation of what the graphs represent.  

What your graphs show is that earnings and ability are positively correlated in a linear fashion.  Your X axis actually represents diminishing ability as you move along it, so the score 1 to 20 represents the amount of uselessness of the person
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Author Comment

by:DColin
ID: 36501471
Hi deighton,

Would an explanation of the potential sine wave be that I have ranked the salespeople on the X-axis based on past performance. If I were to enumerate this rank it would not go 1,2,3 etc. but something like 100, 89,88,87,72,70,65 (best to worst). Do you think the non linearity of a ranking system is causing this?
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by:deighton
ID: 36501528
I doubt if there is a sine wave effect at all.  Seeing the sine wave was a risk of looking at things too closely.  It looks pretty much linear.  Absolute linearity is very unlikely to occur, there will always be some sort of variation.
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