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The returns generated by a sample of five stocks from the Karachi Stock Exchange are given in the exhibit below.
Exhibit: Karachi Stock Exchange Returns – Sample of 5 Stocks
| Stock | Return |
|---|---|
| A | 12% |
| B | 13% |
| C | 5% |
| D | 4% |
| E | 20% |
Using the data above, what is the sample standard deviation of returns?
A
6.53%
B
5.84%
C
7.53%
D
8.34%
Explanation:
The correct answer is A (6.53%).
Calculation Steps:
Calculate the mean: Mean = (0.12 + 0.13 + 0.05 + 0.04 + 0.20) / 5 = 0.54 / 5 = 0.108 or 10.8%
Calculate squared deviations from the mean:
Sum of squared deviations: Total = 0.000144 + 0.000484 + 0.003364 + 0.004624 + 0.008464 = 0.017080
Calculate sample variance: Since this is a sample (not the entire population), we use n-1 in the denominator: Sample variance = 0.017080 / (5 - 1) = 0.017080 / 4 = 0.00427
Calculate sample standard deviation: Sample standard deviation = √0.00427 = 0.06534 or 6.534%
Key Concept: When calculating standard deviation from a sample (as opposed to the entire population), we use (n-1) in the denominator instead of n. This is called Bessel's correction, which provides an unbiased estimate of the population variance. The divisor (n-1) is known as degrees of freedom.