If you ground an economic science on the fact that people choose and you're looking at their action, the only thing you can ever demostrate with action, is that something is better than another. If I pick A over B we can't say - "oh, he valued A 16% more" or "it gave him 16% more utils than B". All you know is A was more valuable, was higher on his preference ranking than B was.

Robert Murphy "The Revolutionary Promise of Austrian Economics Education"