StockIQ will always estimate lost sales based on periods of time that you are out of inventory, so therefore the only option with Lost Sales is whether or not you want the lost sales values applied to your statistical forecast or not.
Using this screen you can modify the default behavior for StockIQ's lost sales. It is available by going to Admin --> System Configuration --> Default Lost Sales Settings.
Calculate Only: StockIQ will calculate estimated lost sales and display them on the chart for your information / awareness, but they are not given to the statistical forecast algorithm
Calculate And Apply: StockIQ will provide calculated lost sale information to the forecast algorithm so that it is taken into account when generating your forecasts.