The longer I teach economics the more I realise all Economic terms are dubious.  Take Merit Good for example, a good underprovided by the free market.  Who gets to decide it is underprovided – cannabis is under-provided in some peoples opinion!  Perhaps then it is the government who decides- but each government makes different decisions.  Thus merit good is a meaningless term unless referenced to morality – now we need at least Kant, Mill, Bentham, et al. to get us out of that mess. Adam Smith it may be remembered was a Professor of Moral Philosophy first.

My science colleagues scoff at this – they have precisely measured units to deal in – but at second glance perhaps they do not.  The definition of a metre has changed over time and even a metre rule expands and contracts with temperature.  If we use wave lengths of atoms as measures  then we have to contend with the different medium the light moves through.  

However the physical sciences do have international bodies to agree on terms. In Economics we do not.  I do notice that terms such as output gap get mangled over time and when I look back at the original papers the author has often been misquoted in High School texts.  There is a system of Chinese whispers in operation here I think.

This is all quite difficult for some students who just want the right answer.  But the better ones get to grips with uncertainty well enough if it is demonstrated.  I think the moral of the story is, do not read your text book uncritically – whoever wrote it!