Facing the Moody Blues

Stock prices slid Friday, sending the Dow Jones Industrial Average below 9,000 for the first time in three weeks. Analysts said equities are vulnerable to wild swings while investors gear up for the corporate pre-announcement season, as companies either downplay losses or emphasize gains. That, plus a lack of major account shifts, caused investors to pull back on shares of marketing-services companies. On the Big Board, IPG experienced the steepest decline, with shares dropping 9.7 percent to close the week at $13.01; Omnicom fell 3.7 percent to $71.91; and British holding company WPP, trading as American Depository Receipts on the Nasdaq, declined 1.2 percent to $39.17.