I've searched a whole lot on the web and there doesn't seem to be a popular strategy of tackling this question:
Given the PI_HAT, Z0, Z1 and Z2 values between 2 individuals, is it possible to narrow down on the possible relationship between the two, in cases where it's not obvious (PO/FS/UN)?
The Zx values are fraction of relatedness measures, as in fraction sharing 0 copies, fraction sharing 1 copy and fraction sharing both copies between 2 individuals. Totally unrelated people would have
Z0 ~ 1 and duplicated samples/identical twins would have
Z2 ~ 1. PO, FS, UN and to an extent HS relationships have well defined values for all Zx as well as PI_HAT
However, once you get to 3rd degree relationships and beyond, (
PI_HAT~0.125), it gets murky. At that point, even the detailed breakdown with the Zx values don't help us figure out what the exact nature of the relationship could be. It could be first cousins, or it could be grandparent-grandchild. Both have
In this case, I wonder if we have a comprehensive listing of all possible relationships for each
PI_HAT fraction (0.125, 0.0625, etc) that I could then combine with clinical information (such as age) and then take a call on the actual relationship?
The closest I've gotten is this table in Wikipedia (and other sources, but Wikipedia is quite good, ironically):
Any help would be appreciated, thank you!