However it is that it was a threshold of another speaker

A such markets drop already occurred

The Dow Jones plunged 9,19 at the meeting, comparably 998,50 points. It is the highest slide in session since at least 1995, since the provider of indices archive data "intraday" (i.e. in session). So far, the most important diving had been registered at the height of the financial crisis, the fall of 2008, just after the bankruptcy of Lehman Brothers. 10 And October 15, 2008, the US index surrendered respectively 8.39 and 8.12. In France, the highest variation in CAC 40 meeting date of 11 September 2001:-10,4. But the "old" of Wall Street saw worse! On the basis of the closing price this time, in full financial crash, October 19, 1987, the Dow Jones industrial average had sunk 22,61! The decline of last Thursday Bell (3.2), although smaller, is notable: it's the strongest decline since the spring of 2009.

Why transactions have not been interrupted

There are "circuit" on scholarships, to temporarily suspend transactions. In the United States, they depend on variation and the schedule on which it occurs. On the New York Stock Exchange, according to the rules in force this quarter, when the Dow loses more than 1,050 points (10), transactions are interrupted for an hour, if the collapse occurs before 2 p.m. (local time). There is no interruption if it occurs after 14: 30 (as Thursday). The duration of the suspension increases according to diving in the index and can go up to a total closure of the stock market. The rules are similar on the Nasdaq. Moreover, there is on Nyse Euronext "human interventions on the values to ensure liquidity and the stability of the market", explains Roland Bellegarde, Executive Vice President in charge of European activities of trading cash and rating of the company. "In the United States, in contrast to other markets electronic as the Nasdaq, Editor's note, we have specialists in values that may intervene to balance the execution of orders if the market packaged.". Intervention depends on the variation and the volatility of each value. This is what explains that several companies have been suspended for 30 to 60 seconds Thursday night. NYSE Euronext provides that there is not, for the moment, of cancellations of transactions on the market, as announced by the Nasdaq.

"trading programs" have aggravated the movement

Irretrievably and invariably Yes. Since the emergence of electronics in the negotiation of the levels of stock in the 1980s, this issue is to each crisis, every crash, every time methane, when indices plunge suddenly beyond reason. And yet the interveners do not undermine field on purpose. Most often, this results from a policy of prudent management. When they are buyers, they prefer to accompany the increase in the values they have in the portfolio, with a "stop-loss", in other words the sales scheduled titles where there would be a reversal markets. These "stop-loss" are moved according to developments in securities and allow, when the scenario is beneficial to ensure added value if the situation comes to radically change and causes a scheduled orders. Most often, they are in the nomenclature of Nyse Euronext orders threshold or range of induction. In the first case, as soon as the sale courses programmed is reached, the titles are assigned to any price below. The latter allows a limit. When several players involved of the kind on the market, in both individual securities that taking the index for reference, there may be an effect snowball. For example, an operator fixed the sale of its portfolio of shares if the CAC 40 breaks 3.390 points. Being large intervener, the massive sale of securities causes a decrease in the French index that comes to pass under the 3.385 points. However it is that it was a threshold of another speaker. The sale of these securities is enabled and the index continues its descent to the underworld. This effect is often amplified when these limits correspond to technical support thresholds, expensive graphics analysts. Once broken, these thresholds can validate lower scenarios or bulls for a few days or months. On the New York Stock Exchange, the "trading programs' represented about 24 of the volumes, the last week of April. Which does not of course the high frequency and algorithmic trading.

What is the high-frequency trading has responsibility

It is not, at present, what triggered precisely Wall Street plunged, but the high-frequency trading is set to the index for a time by regulators. The Chairperson of the SEC repeatedly expressed reservations on this form of negotiation. With the help of automata, proponents of this practice will intervene on inequalities of minimal course, extremely quickly, several times a day and with strong volumes. This trading, benefiting from micro-market inefficiencies, provides an important part of the volumes of the awards. According to estimates by the Reuters news agency, trading high speed would represent 60 of the American volumes. At the weekend, two US Senators asked that regulators are exploring the possibility of identifying high-frequency trading. They ask that the SEC publishes a report to assess the potential risks of the algorithmic trading markets.