The S-value was a statistic used by NAQT to determine wild card qualification for the ICT based on reported SCT statistics. NAQT has never released the formula for the S-value, and no one has ever been able to determine the formula based on the wild card teams invited and the order of waitlist teams. The S-value is known to have had four components: "measures of tossup performance" (likely some variant of tossup points per tossup heard), "[measures of] bonus performance" (likely some variant of bonus conversion), strength of schedule, and overall finish. It is not known how any of these components were implemented in the formula or whether there were additional unreleased components.
No team from a lower playoff bracket can leapfrog a team from a higher playoff bracket for qualification based on the S-value. Other than this stipulation, NAQT awarded wild card bids to teams in descending order of S-value.
In 2004, Patrick King and Jason Mueller took stabs at identifying wild card and waitlist teams based on approximations of S-value. In 2007, Matt Weiner attempted the same thing. None of these attempts were able to accurately divine the initial 32 bids in either division.
Every year, teams received wild card bids while teams that finished ahead of them at the same sectional are left off the waitlist due to having a superior S-value. There has been at least one case where a team believed to have a lower S-value than waitlist teams received a bid so that a team from a lower playoff bracket believed to have a higher S-value could be invited. These scenarios completely baffled experts and stoked the fires of many anti-NAQT partisans.
Beginning with the 2010 SCT, the S-value was replaced by a new statistic, known as the D-value because of Dwight Wynne's role in its development. Unlike the old S-value, all components of the D-value formula are available to the public.