The Psi Index is a system used by the Terran Confederacy and later the Terran Dominion to measure the psionic ability of terrans, a PA Profile having to be established within nine months of birth for all children born within the territory of the former. Under the Dominion, the same system was also used to measure the psionic ability of gestalts; protoss/terran hybrid soldiers.
People with low levels of psychic power can often detect its use, and some can even resist telepathy. A PI rating of 4.5 is too low to reliably project thoughts, and a person with that low a rating is not referred to as a "teep".
The PI score was completely readjusted after Sarah Kerrigan was brought to the new Ghost Program, as she had reached unheard-of levels, forcing this change. With a PI of 10, Kerrigan has the most powerful psi index on record, closely followed by Nova Terra (also with a PI of 10).
|1-2||No psychic powers. Most humans.|
|2-5||Limited powers. Wranglers.|
|5-8||Telepathy. "Teeps". Most ghosts fall between 5 and 6.|
|8-10||May have telekinesis. "Teeks". Extremely rare.|
- Sarco Angelini (10)
- Sarah Kerrigan (pre-infestation) (10)
- Nova Terra (10)
- Jackson Hauler (8.5, prior to spectre enhancement)
- Agent X81505M (8)
- Colin Phash (7.5)
- Gestalt Zero (7+, after protoss gestalt enhancement)
- Delta Emblock (7)
- Stone (7)
- Kath Toom (6.5 prior to enhancement)
- Theodore Pierce (6)
- Tanya Caulfield (5.1)
- Aal Cistler (4.5)
- Malcolm Kelerchian (3.5)
An adjutant rated Sarah Kerrigan as a "class 12 psi signature". A gameplay trailer for Heart of the Swarm listed her as a "class 11 psionic." After being reborn in primal form, an adjutant rated her power as "the highest psi ever recorded" considering it unclassifiable.