In late nineteenth century, the term "political economy" was generally replaced by the term economics,
http://en.wikipedia.org/wiki/Political_economy
Economics isn't a science. Physicists can agree on 99.99 percent of what they talk about, and the other .01 percent is agreed to be unknown or arguable. Economists can barely, just barely, hold a tenuous consensus on things like comparative advantage. The reason economists "get it wrong", is:
1. They want to direct the money into XYZ set of pockets instead of ABC set of pockets, thus they're always "wrong" as for as ABC is concerned, and
2. They don't have the predictive consistency typical of scientists because...they aren't scientists.