Certainly! Let's consider a hypothetical scenario where we have a portfolio of three stocks:
Stock A, Stock B, and Stock C. We want to calculate the standard deviation of the portfolio returns to assess its risk.
To begin, we need historical return data for each stock. Let's assume we have monthly returns for the past year (12 months) for each stock:
Stock A: 2%, 3%, -1%, 4%, 2%, -2%, 1%, 3%, 0%, -1%, 2%, 3%
Stock B: 1%, -1%, 0%, 2%, 1%, -3%, 2%, 1%, 0%, -2%, 1%, 2%
Stock C: -1%, 0%, 3%, -2%, 1%, 2%, -1%, 0%, 2%, 1%, -1%, 3%
Step 1: Calculate the average return for each stock.
To calculate the average return, we sum up all the monthly returns for each stock and divide by the number of months (12 in this case).
Average return of Stock A = (2% + 3% + -1% + 4% + 2% + -2% + 1% + 3% + 0% + -1% + 2% + 3%) / 12 = 1.25%
Average return of Stock B = (1% + -1% + 0% + 2% + 1% + -3% + 2% + 1% + 0% + -2% + 1% + 2%) / 12 = 0.33%
Average return of Stock C = (-1% + 0% + 3% + -2% + 1% + 2% + -1% + 0% + 2% + 1% + -1% + 3%) / 12 = 0.67%
Step 2: Calculate the deviation of each monthly return from the average return.
For each stock, we subtract the average return calculated in Step 1 from each monthly return.
Deviation of Stock A = (2% - 1.25%), (3% - 1.25%), (-1% - 1.25%), (4% - 1.25%), (2% - 1.25%), (-2% - 1.25%), (1% - 1.25%), (3% - 1.25%), (0% - 1.25%), (-1% - 1.25%), (2% - 1.25%), (3% - 1.25%)
Deviation of Stock B = (1% - 0.33%), (-1% - 0.33%), (0% - 0.33%), (2% - 0.33%), (1% - 0.33%), (-3% - 0.33%), (2% - 0.33%), (1% - 0.33%), (0% - 0.33%), (-2% - 0.33%), (1% - 0.33%), (2% - 0.33%)
Deviation of Stock C = (-1% - 0.67%), (0% - 0.67%), (3% - 0.67%), (-2% - 0.67%), (1% - 0.67%), (2% - 0.67%), (-1% - 0.67%), (0% - 0.67%), (2% - 0.67%), (1% - 0.67%), (-1% - 0.67%), (3% - 0.67%)
Step 3: Square each deviation.
To eliminate the negative signs and emphasize the magnitude of deviations, we square each deviation calculated in Step 2.
Squared deviation of Stock A = (2% - 1.25%)^2, (3% - 1.25%)^2, (-1% - 1.25%)^2, (4% - 1.25%)^2, (2% - 1.25%)^2, (-2% - 1.25%)^2, (1% - 1.25%)^2, (3% - 1.25%)^2, (0% - 1.25%)^2, (-1% - 1.25%)^2, (2% - 1.25%)^2, (3% - 1.25%)^2
Squared deviation of Stock B = (1% - 0.33%)^2, (-1% - 0.33%)^2, (0% - 0.33%)^2, (2% - 0.33%)^2, (1% - 0.33%)^2, (-3% - 0.33%)^2, (2% - 0.33%)^2, (1% - 0.33%)^2, (0% - 0.33%)^2, (-2% - 0.33%)^2, (1% - 0.33%)^2, (2% - 0.33%)^2
Squared deviation of Stock C = (-1% - 0.67%)^2, (0% - 0.67%)^2, (3% - 0.67%)^2, (-2% - 0.67%)^2, (1% - 0.67%)^2, (2% - 0.67%)^2, (-1% - 0.67%)^2, (0% - 0.67%)^2, (2% - 0.67%)^2, (1% - 0.67%)^2, (-1% - 0.67%)^2, (3% - 0.67%)^2
Step 4: Calculate the average of the squared deviations.
We sum up all the squared deviations calculated in Step 3 for each stock and divide by the number of months (12 in this case).
Average squared deviation of Stock A = (2% - 1.25%)^2 + (3% - 1.25%)^2 + (-1% - 1.25%)^2 + (4% - 1.25%)^2 + (2% - 1.25%)^2 + (-2% - 1.25%)^2 + (1% - 1.25%)^2 + (3% - 1.25%)^2 + (0% - 1.25%)^2 + (-1% - 1.25%)^2 + (2% - 1.25%)^2 + (3% - 1.25%)^2 / 12
Average squared deviation of Stock B = (1% - 0.33%)^2 + (-1% - 0.33%)^2 + (0% - 0.33%)^2 + (2% - 0.33%)^2 + (1% - 0.33%)^2 + (-3% - 0.33%)^2 + (2% - 0.33%)^2 + (1% - 0.33%)^2 + (0% - 0.33%)^2 + (-2% - 0.33%)^2 + (1% - 0.33%)^2 + (2% - 0.33%)^2 / 12
Average squared deviation of Stock C = (-1% - 0.67%)^2 + (0% - 0.67%)^2 + (3% - 0.67%)^2 + (-2% - 0.67%)^2 + (1% - 0.67%)^2 + (2% - 0.67%)^2 + (-1% - 0.67%)^2 + (0% - 0.67%)^2 + (2% - 0.67%)^2 + (1% - 0.67%)^2 + (-1% - 0.67%)^2 + (3% - 0.67%)^2 / 12
Step 5: Calculate the square root of the average squared deviation.
Finally, we take the square root of the average squared deviation calculated in Step 4 for each stock to obtain the standard deviation.
Standard deviation of Stock A = √(Average squared deviation of Stock A)
Standard deviation of Stock B = √(Average squared deviation of Stock B)
Standard deviation of Stock C = √(Average squared deviation of Stock C)
By following these steps, we can calculate the standard deviation for each stock in our portfolio, providing us with a measure of their individual risk.