Apps. and Interpretation for IBDP Maths Ebook 1 | Page 332

Your Practice Set – Applications and Interpretation for IBDP Mathematics
94
Paper 1 – Two Different Correlation Coefficients
Example
The following table shows the values of the seven observations for two variables X and
Y :
Observation First Second Third Fourth Fifth Sixth Seventh
X 2 4 6 8 10 12 14
Y 1 2 4 8 28 20 62
(a)
Explain why it is not appropriate to use the product moment correlation
coefficient for the above table.
In order to calculate the Spearman’s rank correlation coefficient, the rankings of the
seven observations for two variables X and Y are assigned, where 1 represents the
highest rank and 7 represents the lowest rank.
[1]
(b)
(c)
Find the Spearman’s rank correlation coefficient for the above data set.
Comment on the conclusion of the result in (b).
[2]
[1]
Solution
(a) The values of the seven observations are not linear. A1 N1
(b) rs
� 0.9642857143
(A1) for correct value
(c)
r � 0.964
A1 N2
s
There is a strong agreement between the two
rankings. A1 N1
[1]
[2]
[1]
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