**Contents**

- Semi-Deviation
- Understanding Semi-Deviation
- History of Semi-Deviation in Portfolio Theory
- Downside Deviation
- Understanding Downside Deviation
- Downside Deviation Can Tell You

**Semi-Deviation**

Semi-deviation is a system of measuring the below-mean oscillations in the returns on investment. Semi-deviation is an indispensable dimension to standard divagation or friction. still, unlike those measures, semi-deviation looks only at negative price oscillations. Therefore, semi-deviation is most frequently used to estimate the Downside threat of an investment.

**Understanding Semi-Deviation **

In investing, semi-deviation is used to measure the dissipation of an asset’s price from an observed mean or target value. In this sense, dissipation means the extent of variation from the mean price.

- Semi-deviation is a volition to the standard divagation for measuring an asset’s degree of threat.
- Semi-deviation measures only the below-mean, or negative, oscillations in an asset’s price.
- This dimension tool is most frequently used to estimate parlous investments.

**History of Semi-Deviation in Portfolio Theory**

Semi-deviation was introduced in the 1950s specifically to help investors manage parlous portfolios. Its development is credited to two leaders in the ultramodern portfolio proposition.

- Harry Markowitz demonstrated how to exploit the pars, dissonances, and covariances of the return distributions of means of a portfolio to cipher an effective frontier on which every portfolio achieves the anticipated return for a given friction or minimizes the friction for a given anticipated return. In Markowitz’s explanation, a mileage function, defining the investor’s perceptivity to changing wealth and threat, is used to pick an applicable portfolio on the statistical border.
- A.D. Roy, meanwhile, used semi-deviation to determine the optimum trade-off of threat to return. He did not believe it was doable to model the perceptivity to the threat of a mortal being with a mileage function. rather, he assumed that investors would want the investment with the lowest liability of coming in below a disaster position. Understanding the wisdom of this claim, Markowitz realized two veritably important principles Downside threat is applicable for any investor, and return distributions might be disposed, or not symmetrically distributed, in practice. As similar, Markowitz recommended using a variability measure, which he called a semi-variance, as it only considers a subset of the return distribution.

**Downside Deviation**

Downside Deviation is a measure of Downside threat that focuses on returns that fall below a minimum threshold or minimal respectable return (scar). It’s used in the computation of the Sortino rate, a measure of threat-acclimated return. The Sortino rate is like the Sharpe rate, except that it replaces the standard divagation with the Downside divagation.

**Understanding Downside Deviation **

Standard divagation, the most extensively used measure of investment threat, has some limitations. For illustration, it treats all diversions from the average, whether positive or negative as the same. still, investors are generally only bothered by negative surprises. Downside divagation resolves this issue by fastening solely on the Downside threat. still, downside divagation isn’t the only way to look at losses. Maximum drawdown (MDD) is another way of measuring Downside threat. A fresh advantage of Downside divagation over standard divagation is that downside divagation can also be acclimatized to specific objects. It can change to fit the threat biographies of different investors with colorful situations of minimal respectable return. The Sortino and Sharpe rates enable investors to compare investments with different situations of volatility, or in the case of the Sortino rate, Downside threat. Both rates look at redundant return, the quantum of return above the threat-free rate. Short-term Treasury securities frequently represent the threat-free rate. Suppose two investments have the same anticipated return, say 10. still, one has a Downside divagation of 9, and the other has a Downside divagation of 5 where the dollar is the better investment.

**Downside Deviation Can Tell You **

Downside divagation gives you a better idea of how much investment can lose than standard divagation alone. Standard divagation measures volatility on the downside and the Downside, which presents a limited picture. Two investments with the same standard diversions are likely to have different Downside diversions. Downside divagation can also tell you when a” parlous” investment with a high standard divagation is likely safer than it looks. Consider an investment that pays 40 half the time and still pays 20 in lower successful times. Such an investment would have a much more advanced standard divagation than one that simply paid 5 every time. still, many people would say that getting paid 5 every time was safer. Both of these investments would have a Downside divagation of zero using 5 as the minimal respectable return (scar). That tells us that they’re both impeccably safe investments.