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A portfolio manager is trying to determine the correlation between the return of two assets. Given the following data about the yearly returns of the stocks, he decides to calculate the Kendall's τ correlation coefficient for the returns of these assets.
| Year | Return of Asset X | Return of Asset Y |
|---|---|---|
| 1 | 3% | 8% |
| 2 | 1% | 5% |
| 3 | –4% | 6% |
| 4 | 5% | 2% |
| 5 | 2% | 9% |
What is Kendall's τ correlation coefficient for the returns of the two assets?
A
-0.1
B
-0.2
C
0
D
0.1
Explanation:
Kendall's τ measures the ordinal association between two variables. It is calculated as:
τ = (number of concordant pairs - number of discordant pairs) / (total number of pairs)
Total number of pairs = C(5,2) = 10
Concordant pairs (both variables move in same direction):
(3,8) vs (1,5): X decreases (3→1), Y decreases (8→5) → Concordant
(3,8) vs (-4,6): X decreases (3→-4), Y decreases (8→6) → Concordant
(3,8) vs (5,2): X increases (3→5), Y decreases (8→2) → Discordant
(3,8) vs (2,9): X decreases (3→2), Y increases (8→9) → Discordant
(1,5) vs (-4,6): X decreases (1→-4), Y increases (5→6) → Discordant
(1,5) vs (5,2): X increases (1→5), Y decreases (5→2) → Discordant
(1,5) vs (2,9): X increases (1→2), Y increases (5→9) → Concordant
(-4,6) vs (5,2): X increases (-4→5), Y decreases (6→2) → Discordant
(-4,6) vs (2,9): X increases (-4→2), Y increases (6→9) → Concordant
(5,2) vs (2,9): X decreases (5→2), Y increases (2→9) → Discordant
τ = (4 - 6) / 10 = -2 / 10 = -0.2
Therefore, Kendall's τ correlation coefficient is -0.2, indicating a weak negative correlation between the returns of Asset X and Asset Y.