In socionics, it is a blend of the quadra types with how they play out in specific information elements. I look for evidence of these as well as evidence that the desired interrelations to the non-ego blocks hold. In short, I type by information elements all fitting together in the rough pattern they are meant to, using other dichotomies/forms of cognition/etc as supplements for detection of the required patterns.

That said, I experience doubt in typings and am still not decided on my own.