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Python for Finance

We discussed this concept already. However, for completeness, in this chapter we mention it again. One issue with using standard deviation of returns as a risk measure is that the positive deviation is also viewed as bad. The second issue is that the deviation is from the average instead of a fixed benchmark, such as a risk-free rate. To overcome these shortcomings, Sortino (1983) suggests the lower partial standard deviation, which is defined as the average of squared deviation from the risk-free rate conditional on negative excess returns, as shown in the following formula:
Because we need the risk-free rate in this equation, we could generate a Fama-French dataset that includes the risk-free rate as one of their time series. First, download their daily factors from http://mba.tuck.dartmouth.edu/pages/faculty/ken.french/data_library.html. Then, unzip it and delete the non-data part at the end of the text file. Assume the final text file...
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