Other shoppers will be pleased by the sprouting of chic fashion and jewelry boutiques in Lisbon and Porto, as well as wine shops and cellars stocking Portugal's famous fortified wines.
There are several regional shopping attractions.
There could be many influences on what is happening and these influences could interact in nonlinear ways such that a unit of change in the input can be associated with quite different changes in the output, sometimes increasing it, sometimes decreasing it, and sometimes having no discernible effect.