Frederic Bastiat famously argued that:

There is only one difference between a bad economist and a good one: the bad economist confines himself to the visible effect; the good economist takes into account both the effect that can be seen and those effects that must be foreseen.

We see what Bastiat wrote about all around us. When the UK Department of Trade and Industry gave a subsidy to Rover Cars in 1998, it saved jobs. How many more jobs would have been created had that money been left in the hands of taxpayers and used for more productive uses?

When the US government introduced steel tariffs in 2002, it ended up saving 5000 jobs. But 26,000 jobs were lost elsewhere in the economy as a result.

The losers of protectionism and subsidy are often dispersed wide throughout the economy and throughout a range of industries. It is therefore more difficult to see the losers than the winners. But just because the losers are not as visible - or not as politically connected - useful economic analysis must remember to factor them in.