The Down Jones industrial average closed its worst week this year Friday, falling 1.7 percent overall, the worst decline since January. Much of that activity—83 percent of it, in fact—was attributable to a drop in JPMorgan Chase stock after the bank announced it had lost $2 billion in a series of trades. JPMorgan’s stock fell $3.78. The Standard & Poor’s 500 dipped 4.6 points, while the NASDAQ lifted slightly. JPMorgan has said that it could suffer as much as $1 billion in additional second-quarter losses. Analysts said that the bad news for the Dow may be more a blip than anything else, as the market looked strong overall in the first quarter.