PMCC vs Standard Deviation

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Fuenciado
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#1
Report Thread starter 7 years ago
#1
Could someone help/explain this to me. The mark scheme didn't really help at all.

A student had 2 sets of bivariate data. He found the standard deviation and pmcc of each set.

Set A: pmcc = 0.9....sd = 1
Set B: pmcc = 1.......sd = 0.9

Why can the results for set A be correct but not both results for set B?
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ghostwalker
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#2
Report 7 years ago
#2
(Original post by Fuenciado)
Could someone help/explain this to me. The mark scheme didn't really help at all.

A student had 2 sets of bivariate data. He found the standard deviation and pmcc of each set.

Set A: pmcc = 0.9....sd = 1
Set B: pmcc = 1.......sd = 0.9

Why can the results for set A be correct but not both results for set B?
What's "sd" here? Standard deviation of what?
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davros
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#3
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#3
(Original post by Fuenciado)
Could someone help/explain this to me. The mark scheme didn't really help at all.

A student had 2 sets of bivariate data. He found the standard deviation and pmcc of each set.

Set A: pmcc = 0.9....sd = 1
Set B: pmcc = 1.......sd = 0.9

Why can the results for set A be correct but not both results for set B?
Do you have a link to the original question and to the mark scheme?
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Fuenciado
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#4
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#4
(Original post by davros)
Do you have a link to the original question and to the mark scheme?

Wasn't working as an image so I've done it as an attachment
Attached files
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Protoxylic
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#5
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#5
(Original post by Fuenciado)
Wasn't working as an image so I've done it as an attachment
R sub s is spearman's rank, not standard deviation. Lower case sigma is standard deviation.
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Fuenciado
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#6
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#6
(Original post by Protoxylic)
R sub s is spearman's rank, not standard deviation. Lower case sigma is standard deviation.
Yeah I know, I didn't even notice that I'd called it the wrong thing.
I've done like 26 hours of stats in the last 3 days , I think my brain is broken.
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DFranklin
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#7
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#7
So, now you know it's Spearman's Rank, do you know how to procede?
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Fuenciado
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#8
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#8
(Original post by DFranklin)
So, now you know it's Spearman's Rank, do you know how to procede?
Not really
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ghostwalker
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#9
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#9
(Original post by Fuenciado)
Not really
Pmcc is a measure of how good a fit a linear realationship is, with "1" (or "-1") being a perfect fit.

Spearmans is a measure of how good a fit a monotonic relationship is, with "1! (or "-1") being a perfect fit.

With that in mind, which of the two sets are giving you problems?
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DFranklin
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#10
Report 7 years ago
#10
In case ghostwalker's post is a little too tech-speak:

If you plot the points on an X,Y scatter diagram, then PMCC = 1 means the points lie on a straght line, while SRCC = 1 means the points always go "up" as you increase X. (i.e. Y is an increasing function of X).
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