S1 Jan 05 Watch

Christophicus
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#1
Report Thread starter 12 years ago
#1
Mark scheme 2c
How can Seaview have negative skew if Q2-Q1<Q3-Q2
and Northcliffe positive skew when Q2-Q1=Q3-Q2

:confused:

http://www.school-portal.co.uk/Group...ourceId=197165
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Chewwy
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#2
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well, as i'm sure you can guess, they're probably looking at the full range. but hey, i'm equally confused.
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Christophicus
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#3
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#3
3e They divided by n for a sample. I'm really worried I'm not gonna get the marks cos of some crappy mark scheme.
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k10k
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#4
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... they also have in my MS: Northcliffe symmetrical, Seaview positive skew (quartiles) as well as the other statement. Pearson Mode Skewness (Mean-mode)/standard deviation gives a different value depending on which mode value you use (since there are two I think for Seaview?)

There's three ways to calculate the skewness, the moment method, quartiles method... and the one I used. They do sometimes give different answers. Discrete values always cause problems. You would have got your marks however.

3e) I know I felt the same way, in most other MS they allow both methods, however the method with the n-1 is not specifically in the syllabus just the book Heinamann I think. Just forget about the n-1 fact for a sample vs n for a population. They don't care!
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k10k
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#5
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I think it's a bimodal distribution so it disturbs our text book theory.
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