Social constructionism

How the hell...? Is it possible to study a social construct that does exist in the head of the researcher but not in the head of the researched?
Of course it is, but it makes research even more complicated.

If I'd measure the leaf size of Portuguese cabbage I could build the construct, define it my way and for the purposes of my research and measure leaves according to it. It would be very consistent.

But now I'm studying different types of farming and different types of livelihoods and people's opinion about them. But if everyone has different definitions, for "family farming" for example, I somehow loose the ground beneath my feet if I compare people's opinions about different constructs as if they were about the same construct. Of course it is in itself an interesting study to find out about the existing constructs, but will I be able to conclude anything about the consequences of those constructs on the sustainability of agriculture?

I would probably have to present my construct to the interviewees and ask their opinion about it...

I'm writing these relfexions because I find the implications of (a mild form of) social constructionism fascinating...