After experiencing minor losses during the middle of the week, the Dow Jones Industrial Average managed to post modest gains Friday, ending the week up. But ad holding company stocks saw declines as the week ended, as analysts said the recovery from the ad recession is still moving in fits and starts. “There is still some uncertainty as to how strong the recovery is going to be, and that’s having a slight dampening effect on stocks,” one ad analyst said. On the Big Board, Omnicom shares declined 1.7 percent to close the week at $77.95, while IPG’s stock price slid 4.9 percent to $14.31. WPP, trading as American Depository Receipts on the Nasdaq, fell 1.7 percent to finish at $46.05.