Mean Reversion

Mean Reversion

Mean reversion is a mathematical methodology sometimes used for stock investing, but it can be applied to other processes. In general terms the idea is that both a stock's high and low prices are temporary, and that a stock's price will tend to have an average price over time.

Mean reversion involves first identifying the trading range for a stock, and then computing the average price using analytical techniques as it relates to assets, earnings, etc.

When the current market price is less than the average price, the stock is considered attractive for purchase, with the expectation that the price will rise. When the current market price is above the average price, the market price is expected to fall. In other words, deviations from the average price are expected to revert to the average.

The Standard deviation of the most recent prices (e.g., the last 20) is often used as a buy or sell indicator.

Stock reporting services (such as Yahoo! Finance, MS Investor, Morningstar, etc.), commonly offer moving averages for periods such as 50 and 100 days. While reporting services provide the averages, identifying the high and low prices for the study period is still necessary.

Mean reversion has the appearance of a more scientific method of choosing stock buy and sell points than charting, because precise numerical values are derived from historical data to identify the buy/sell values, rather than trying to interpret price movements using charts (charting, also known as technical analysis).

Arbitrage

Arbitrage

In economics and finance, arbitrage (IPA: /ˈɑrbɨtrɑːʒ/) is the practice of taking advantage of a price difference between two or more markets: striking a combination of matching deals that capitalize upon the imbalance, the profit being the difference between the market prices. When used by academics, an arbitrage is a transaction that involves no negative cash flow at any probabilistic or temporal state and a positive cash flow in at least one state; in simple terms, it is the possibility of a risk-free profit at zero cost.

Conditions for arbitrage

Arbitrage is possible when one of three conditions is met:
The same asset does not trade at the same price on all markets (the "law of one price").
Two assets with identical cash flows do not trade at the same price.
An asset with a known price in the future does not today trade at its future price discounted at the risk-free interest rate (or, the asset does not have negligible costs of storage; as such, for example, this condition holds for grain but not for securities).

Arbitrage is not simply the act of buying a product in one market and selling it in another for a higher price at some later time. The transactions must occur simultaneously to avoid exposure to market risk, or the risk that prices may change on one market before both transactions are complete. In practical terms, this is generally only possible with securities and financial products which can be traded electronically, and even then, when each leg of the trade is executed the prices in the market may have moved. Missing one of the legs of the trade (and subsequently having to trade it soon after at a worse price) is called 'execution risk' or more specifically 'leg risk'

In the simplest example, any good sold in one market should sell for the same price in another. Traders may, for example, find that the price of wheat is lower in agricultural regions than in cities, purchase the good, and transport it to another region to sell at a higher price. This type of price arbitrage is the most common, but this simple example ignores the cost of transport, storage, risk, and other factors. "True" arbitrage requires that there be no market risk involved. Where securities are traded on more than one exchange, arbitrage occurs by simultaneously buying in one and selling on the other.

See rational pricing, particularly arbitrage mechanics, for further discussion.

Changes in reserves

Changes in reserves

The quantity of foreign exchange reserves can change as a central bank implements monetary policy.A central bank that implements a fixed exchange rate policy may face a situation where supply and demand would tend to push the value of the currency lower or higher (an increase in demand for the currency would tend to push its value higher, and a decrease lower). In a flexible exchange rate regime, these operations occur automatically, with the central bank clearing any excess demand or supply by purchasing or selling the foreign currency. Mixed exchange rate regimes ('dirty floats', target bands or similar variations) may require the use of foreign exchange operations (sterilized or unsterilized to maintain the targeted exchange rate within the prescribed limits .

Foreign exchange operations that are unsterilized will cause an expansion or contraction in the amount of domestic currency in circulation, and hence directly affect monetary policy and inflation: An exchange rate target cannot be independent of an inflation target. Countries that do not target a specific exchange rate are said to have a floating exchange rate, and allow the market to set the exchange rate; for countries with floating exchange rates, other instruments of monetary policy are generally preferred and they may limit the type and amount of foreign exchange interventions. Even those central banks that strictly limit foreign exchange interventions, however, often recognize that currency markets can be volatile and may intervene to counter disruptive short-term movements.

To maintain the same exchange rate if there is increased demand, the central bank can issue more of the domestic currency and purchase the foreign currency, which will increase the sum of foreign reserves. In this case, the currency's value is being held down; since (if there is no sterilization) the domestic money supply is increasing (money is being 'printed'), this may provoke domestic inflation (the value of the domestic currency falls relative to the value of goods and services).

Since the amount of foreign reserves available to defend a weak currency (a currency in low demand) is limited, a foreign exchange crisis or devaluation could be the end result. For a currency in very high and rising demand, foreign exchange reserves can theoretically be continuously accumulated, although eventually the increased domestic money supply will result in inflation and reduce the demand for the domestic currency (as its value relative to goods and services falls). In practice, some central banks, through open market operations aimed at preventing their currency from appreciating, can at the same time build substantial reserves.

In practice, few central banks or currency regimes operate on such a simplistic level, and numerous other factors (domestic demand, production and productivity, imports and exports, relative prices of goods and services, etc.) will affect the eventual outcome. As certain impacts (such as inflation) can take many months or even years to become evident, changes in foreign reserves and currency values in the short term may be quite large as different markets react to imperfect data.