# Downside deviation python

PD: In addition, I found this other comment which summarizes what I meant link :. ShaktiRathore It was my understanding that the downside deviation i. I am interested in Semivariance because I want to use it to compute the Sortino Ratio.

I found an article on Sortino which answers to my question. From a practical point of view, the calculation must take into account all the data substituting a zero for those values above or equal to your targetnot just the observations below the target.

This is so the Sortino ratio will return a higher value that Sharpe ratio when there are many observations above the target. If you consider a reduced sample excluding zeros in the denominator the Sortino will be lower than Sharpe, which is not the idea of this ratio.

Throwing away the zero underperformance data points results in the same target downside deviation for both return streams, but clearly the first return stream has much less downside risk than the second. So, I should not discard any zero because I will be reducing the data, which results in a lower Sortino than Sharpe ratio.

Finally, I would like to point it out that I found papers and books one was from the CFA that compute semivariance using the first method throwing away the zeros.

So I think confusion around it is still there. Sign up to join this community. The best answers are voted up and rise to the top.

Home Questions Tags Users Unanswered. Semivariance calculation downside deviation Ask Question. Asked 2 years ago. Active 2 years ago. Viewed 2k times.By Apoorva Singh and Rekhit Pachanekar. We all know that you should never put all your eggs in one basket. Hence, we try to build a portfolio consisting of different financial instruments.

At the same time, you might develop different strategies to balance various measures such as risk, volatility, expected returns etc. But how do you say one strategy is better than the one? The normal answer, i.

Some strategies might be directional, some market neutral and some might be leveraged which makes annualized return alone a futile measure of performance measurement. Also, even if two strategies have comparable annual returns, the risk is still an important aspect that needs to be measured.

With this in mind, William Sharpe introduced a simple formula to help compare different portfolios and help us find the most feasible of them all. Sharpe ratio is a measure for calculating risk-adjusted return. It is the ratio of the excess expected return of investment over risk-free rate per unit of volatility or standard deviation.

Let us see the formula for Sharpe ratio which will make things much clearer. The sharpe ratio calculation is done in the following manner. Where, x is the investment Rx is the average rate of return of x Rf is the risk-free rate of return StdDev x is the standard deviation of Rx. Once you see the formula, you will understand that we deduct the risk-free rate of return as this helps us in figuring out if the strategy makes sense or not. Some of you would recognise this as the risk-adjusted return.

In the denominator, we have the standard deviation of the average return of the investment. It helps us in identifying the volatility as well as the risk associated with the investment. Thus, the Sharpe ratio helps us in identifying which strategy gives better returns in comparison to the volatility. There, that is all when it comes to sharpe ratio calculation. You have devised a strategy and created a portfolio of different stocks. Now, you change certain parameters and pick different financial instruments to create another portfolio, Portfolio B.

Thus, according to the Sharpe Ratio calculation, we should consider Portfolio B because even though the expected return is less than portfolio B, the volatility of portfolio B is less than portfolio A and thus, is less risky. Currently, most exchange-traded funds provide the Sharpe ratio for their investments on their websites as well.

Sharpe Ratio can be used in many different contexts such as performance measurement, risk management and to test market efficiency. If there are N trading periods in a year, the annualised Sharpe is calculated as:. Sharpe ratio can be calculated by following these simple steps:. Now, as per the definition, the numerator, which is the mean of PnL gets multiplied by N when you consider all trades. For high-frequency strategies, a large number of small successful trades for specific amounts smoothen the PnL curve and the standard deviation approaches to zero which significantly spikes the Sharpe ratio, such that it might range in double digits. Most Quantitative hedge funds ignore strategies with annualized Sharpe ratio less than 2. For a retail algorithmic trader, an annualized Sharpe ratio greater than 2 is pretty good.

For high-frequency trading, as discussed, the ratio can go up in double digits as well, especially for opportunity-driven but not highly scalable strategies. The ratio is used by an individual when they are adding a new financial instrument to an existing portfolio, and they want to check how it impacts the portfolio.Calculating downside deviation can help you identify and steer clear of investments that are unlikely to meet these expectations.

A lower percentage suggests less risk of losing money. An investment with a high downside deviation has a habit of cranking out poor returns and might put a dent in your portfolio.

Assume the other monthly returns in decimal form were Identify the monthly returns that were less than your MAR, which is the minimum monthly return you require in order to own the investment. In this example, assume you require a 1 percent, or 0. Subtract each return you identified in Step 3 from your MAR. Square each result. In this example, subtract Square 0. Subtract and square the other result to get 0. Add each squared result. Divide that result by the number of returns you calculated in Step 2.

In this example add 0. Divide 0. Calculate the square root of your result. Concluding the example, calculate the square root of 0.

Multiply 0. This investment has a lower tendency of generating returns less than your 1 percent MAR than an investment with, say, a 9 percent downside deviation. A high downside deviation represents a greater risk of bad returns. Tips You can calculate downside deviation using any periodic returns, such as quarterly or annual returns, and can use more than six periods in your calculation.

The more periods you use, the more accurate your result will be. Make sure each downside deviation was calculated using the same type of periodic returns. Video of the Day. Brought to you by Sapling.Click to Download Workbook: Sortino Ratio. Before we delve into an explanation of how the Sortino Ratio is calculated, you should probably understand an extremely popular risk-adjusted measure: the Sharpe Ratio. The Sharpe ratio is a very popular risk-adjusted measure.

With the Sharpe ratio, we are looking at volatility or the standard deviation of a portfolio or fund. The ratio is calculated as:. A value of 1 is considered acceptable, while a value above 2 is considered exceptional. The Sortino Ratio is quite similar but far less popular. Instead of standard deviation, the Sortino Ratio uses downside deviation within the denominator of the calculation.

Downside Deviation is essentially the standard deviation of all negative returns of the portfolio.

## Sortino ratio

We also selected a minimum acceptable return as well. This will be explained within the Excel calculation. The idea with the Sortino Ratio is that examining positive returns or upside volatility is irrelevant, as investors theoretically should be concerned more with downside deviation.

This concept is better explained in Excel, although we examine how this can be done in R with the PerformanceAnalytics package also. First, we need to generate portfolio returns.

I did this in R for a variety of assets in monthly terms. The key with the Sortino Ratio is that we have to choose a minimum acceptable return. The idea of choosing a minimum acceptable return MAR is that any return above the MAR is not included for the purpose of calculating the risk-adjusted measure. We can first calculate the excess returns which are are the portfolio returns for each month subtracted from the MAR.

We can then select only negative excess returns from the series with a simple if statement. First, we need to obtain the data and return a series of aggregate portfolio returns. I am assuming a portfolio of 10 assets all with equal weights. Next, we can calculate each ratio quite easily with built-in PerformanceAnalytics functions. Note for the risk-free, I am obtaining data for a 6-month treasury bill over the last year and taking the arithmetic mean as my risk-free rate.

The output of the calculation is displayed below with the source code beneath it. Note for the Sharpe ratio we are asked to input a confidence interval as well. In the output, we receive three Sharpe ratios all using different risk metrics. Focus on the StdDev Sharpe which is most commonly used. Explaining each of those ratios is outside the scope of this post. Your email address will not be published. Click to Download Workbook: Sortino Ratio Before we delve into an explanation of how the Sortino Ratio is calculated, you should probably understand an extremely popular risk-adjusted measure: the Sharpe Ratio.

Sharpe Ratio: The Sharpe ratio is a very popular risk-adjusted measure. Sortino Ratio: The Sortino Ratio is quite similar but far less popular. The idea with the Sortino Ratio is that examining positive returns or upside volatility is irrelevant, as investors theoretically should be concerned more with downside deviation This concept is better explained in Excel, although we examine how this can be done in R with the PerformanceAnalytics package also.Downside deviation, similar to semi deviation, eliminates positive returns when calculating risk.

Instead of using the mean return or zero, it uses the Minimum Acceptable Return as proposed by Sharpe which may be the mean historical return or zero. To calculate it, we take the subset of returns that are less than the target or Minimum Acceptable Returns MAR returns and take the differences of those to the target.

We sum the squares and divide by the total number of returns to get a below-target semi-variance. SemiDeviation or SemiVariance is a popular alternative downside risk measure that may be used in place of standard deviation or variance.

In many functions like Markowitz optimization, semideviation may be substituted directly, and the covariance matrix may be constructed from semideviation or the vector of returns below the mean rather than from variance or the full vector of returns. In semideviation, by convention, the value of n is set to the full number of observations. In semivariance the the value of n is set to the subset of returns below the mean. It should be noted that while this is the correct mathematical definition of semivariance, this result doesn't make any sense if you are also going to be using the time series of returns below the mean or below a MAR to construct a semi-covariance matrix for portfolio optimization.

Sortino recommends calculating downside deviation utilizing a continuous fitted distribution rather than the discrete distribution of observations. This would have significant utility, especially in cases of a small number of observations.

He recommends using a lognormal distribution, or a fitted distribution based on a relevant style index, to construct the returns below the MAR to increase the confidence in the final result. Hopefully, in the future, we'll add a fitted option to this function, and would be happy to accept a contribution of this nature. Sortino, F. Performance Measurement in a Downside Risk Framework. Journal of Investing. Fall Plantinga, A. July 19, Returns the standard deviation, a measure of the spread of a distribution, of the array elements.

The standard deviation is computed for the flattened array by default, otherwise over the specified axis. Axis or axes along which the standard deviation is computed. The default is to compute the standard deviation of the flattened array. If this is a tuple of ints, a standard deviation is performed over multiple axes, instead of a single axis or all the axes as before.

Type to use in computing the standard deviation. For arrays of integer type the default is float64, for arrays of float types it is the same as the array type.

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Alternative output array in which to place the result. It must have the same shape as the expected output but the type of the calculated values will be cast if necessary.

### How to Calculate Downside Deviation

Means Delta Degrees of Freedom. The divisor used in calculations is N - ddofwhere N represents the number of elements. By default ddof is zero. If this is set to True, the axes which are reduced are left in the result as dimensions with size one. With this option, the result will broadcast correctly against the input array. If the default value is passed, then keepdims will not be passed through to the std method of sub-classes of ndarrayhowever any non-default value will be. If out is None, return a new array containing the standard deviation, otherwise return a reference to the output array.

The standard deviation is the square root of the average of the squared deviations from the mean, i. The average squared deviation is normally calculated as x. If, however, ddof is specified, the divisor N - ddof is used instead. Note that, for complex numbers, std takes the absolute value before squaring, so that the result is always real and nonnegative. For floating-point input, the std is computed using the same precision the input has.

Depending on the input data, this can cause the results to be inaccurate, especially for float32 see example below. Specifying a higher-accuracy accumulator using the dtype keyword can alleviate this issue. New in version 1. See also varmeannanmeannanstdnanvar numpy. Previous topic numpy.

Last updated on Jul 26, Created using Sphinx 1.Returns of the strategy as a percentage, noncumulative. Time series with decimal returns. For increased numerical accuracy, convert input to log returns where it is possible to sum instead of multiplying. Daily returns of the strategy, noncumulative. Periodic returns of the strategy, noncumulative. Value ignored if annualization parameter is specified. Defaults are:. Used to suppress default values available in period to convert returns into annual returns.

## How to Calculate the Sortino Ratio

Value should be the annual frequency of returns. Calmar ratio drawdown ratio as float. Returns numpy. Minimum acceptance return of the investor. Threshold over which to consider positive vs negative returns. It will be converted to a value appropriate for the period of the returns. An annual minimum acceptable return of will translate to a minimum acceptable return of 0.

Enter 1 if no time period conversion is necessary. Series or pd. Daily noncumulative returns of the factor to which beta is computed. Usually a benchmark such as the market. This is in the same style as returns. Constant risk-free return throughout the period. For example, the interest rate on a three month us treasury bill.

Determines R-squared of a linear fit to the cumulative log returns. Computes an ordinary least squares linear fit, and returns R-squared. API Reference. Parameters: returns : pandas. Series Returns of the strategy as a percentage, noncumulative.

Example: - 07 - 16 - 0.