Say you're trying to get the closing price of a particular stock. You don't want to use MOC orders, so you try to execute as close to 4:00 pm as possible. In this case, is there any reason why you would tend to have negative slippage? Say your order is executed at 3:59 pm. In the final minute of trading, the stock can move either up or down with equal probability because of such a short time period, so your slippage can be either positive or negative. Do you agree? Assume that your order size does not move the market.