Dow Jones plunged 1.1% on Monday, thus extending the decline from its January peak to over 20%. With this, the oldest of Wall Street's 3 main indices met the common definition of a bear market. S&P Dow Jones Indices Senior Analyst Howard Silverblatt said that a plunge of 20% or more from a high, followed by a 20% gain from the lower level, would leave an index still below its earlier peak.