They can also be used for tests for structural change, right, what we're going to do is to say during peacetime  right, we'll estimate our model, we'll then estimate our model during wartime and we're going to assume that the coefficients or the income and price elasticity  mark, don't change during between peace and wartime, all that happens is as they intercept this model shifts, right, now you may thinks that's not particularly er attractive, you might expect the price of income elasticities to change between two periods and we could actually use dummy variables to see whether that is the case, right, however, we'll get very similar results, right, if you just use a slope dummy so it'd intercept dummy, right, and all that's going to do is to say, well the model runs like this in peacetime, right, and then wartime it suddenly shifts up or down depending on the effect of er of the war on textile consumption.