i want to clarify my comment about the spx not accounting for dividends. the dividend is lost, from comparing the index against the total return index, but the drop in price of the index components, on their ex-date, affects the index. the yield is currently 1.25%, based on spy. if the components ex-dates were evenly distributed, it amounts to about $.22 per trading day. the actual daily price change, and how to model it, is difficult to determine.