Sum Typing is not really that much new, as some tests indirectly use it. The idea is plain simple: Attribute a stack – any stack at the beginning – for each type, just for example INFP = 1.5*Fi + 1*Ne + 0.5*Si – 0.5*Te. And then, using the test results, calculate for which type the person have the most points and – viola! – that’s the person type.
It can be any stack, but, of course, if the stack is screwed up and unrealistic, the results will end up badly. It can even works for less or more than 16 types. Just for example:
Sensor: Se+Si
Intuitive: Ne+Ni
And goes on.
I had a look on some few dozens of results on Sakinorva, forum test and Dario Nardi test, and based on how people type themselves on their profiles, I had tuned the best fit stack (that can have some theory) for every type. I found out that the achile heels is quite unreliable (the Te for INFP, Ne for ISFJ, etc…). Here it is the final stack:
Weights: 3-2-1
INFP: Fi-Ne-Ni
INFJ: Ni-Fe-Fi
INTP: Ti-Ne-Ni
INTJ: Ni-Te-Ti
ENFP: Ne-Fi-Fe
ENTP: Ne-Ti-Te
ENFJ: Fe-Ni-Ne
ENTJ: Te-Ni-Ne
ISFP: Fi-Se-Si
ISTP: Ti-Se-Si
ISFJ: Si-Fe-Fi
ISTJ: Si-Te-Ti
ESTP: Se-Ti-Te
ESTJ: Te-Si-Se
ESFP: Se-Fi-Fe
ESFJ: Fe-Si-Se
Some observations for this stack:
– Of course it isnt fixed, Im not meaning that INFPs always and must have Fi as a first, Ne as a second and Ni as tertiary function. Its an “ideal INFP” that has that, however my ideal INFP is not that much unrealistic (just go to a thread of cognitive function tests and you will see).
– The tertiary is quite personal and test results are distorted by some things. For example, the best fit for ENFP 7 is Ne-Se-Fi or Ne-Fi-Se instead.
– Every cousin share at least the first function or two functions (there is no “INTJ and INTP doesnt share functions” thing).
– When a person have a borderline on the first function department, for example ENFJ with borderline in F/T, this method tends to struggle a bit but it still works, mostly.
Typology Triad 