NEW YORK, Sept 23 (Reuters) - U.S. stock index futures slightly added to losses on Thursday after data showed an unexpected rise in initial applications for unemployment insurance in the latest week.
S&P 500 futures fell 11.3 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures dropped 84 points and Nasdaq 100 futures lost 17 points. (Editing by Theodore d'Afflisio)