For a country which is still more nearly self-sufficient, like the United States, productivity counts for nearly everything and terms of trade for very little in determining the average standard of living. On the other hand, a family in an advanced economy exchanges a very high proportion of its output (which consists mostly of services) for things bought in the market. The rate of exchange between its services and the things it buys is therefore of nearly equal importance with its productivity in determining how good a living it gets.