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Section 2: Bivariate Data



























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WARNING: a STRONG positive correlation doesn't necessarily mean that one factor CAUSES the
other.

NOTE:
When asked in an exam question to explain why the student is wrong if he/she suggests a
positive/ negative correlation then state:
1. Correlation does not imply causation
2. There must be a third causal…

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However, if one or both of your variables is skewed (i.e. asymmetrical) or bimodal (i.e. data
points occur in 2 groups) then this test could give a false result.


WHEN CONDUCTING A PMCC TEST:
1. State the null hypothesis and alternative hypothesis for the test:

Onetailed test H0: = 0…

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USING THE FORMULA:
Example: At a dog show, two judges ranked 8 of the Labradors (AH) in the following order.
Calculate the rs and comment on your result.

POSITION 1ST 2ND 3RD 4TH 5TH 6TH 7TH 8TH
JUDGE 1 B C E A D F G H
JUDGE 2 C…

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If x falls within the range if data, then the yvalue is reliable. This is called INTERPOLATION.
If x falls outside the range of data, then the estimated yvalue is unreliable. This is called
EXTRAPOLATION.

WHY IS PMCC A BETTER TEST THAN SPEARMANS RANK?

PMCC is better since it takes…

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