Apps. and Interpretation for IBDP Maths Ebook 1 | Page 329

93
Paper 1 – Spearman’s Rank Correlation Coefficient
Example
The table below shows the ranking of eight universities suggested by two educational
experts, where 1 represents the highest ranking and 8 represents the lowest ranking:
University A B C D E F G H
Expert 1 2 3 1 7 8 4 4 6
Expert 2 1 2 2 8 7 4 6 5
(a)
Write down
(i)
the average equal ranks of the University F and the University G in Expert
1’s ranking;
(b)
(c)
(ii) the average equal ranks of the University B and the University C in Expert
2’s ranking.
[2]
Find the Spearman’s rank correlation coefficient for the above data set.
[2]
Comment on the conclusion of the result in (b).
[1]
Solution
(a) (i) 4.5 A1 N1
22
(ii) 2.5 A1 N1
(b) rs
� 0.8915662651
(A1) for correct value
(c)
r � 0.892
A1 N2
s
There is a strong agreement between the two
experts. A1 N1
[2]
[2]
[1]
www.seprodstore.com
319