QSI is an analytical method used to allocate estimated demand across multiple competing itineraries on a given origin–destination (O&D) pair. The process involves identifying all viable routing options from the flight schedule—considering carriers, flight numbers, times of day, aircraft types, day-of-week operations, and connection patterns—and assigning each itinerary a weighted service quality score.
The scoring system reflects passenger preferences, giving higher weights to more desirable service characteristics such as nonstops over connections, wide-body aircraft over narrow-body aircraft, shorter flight time over longer flight time.
Each carrier accumulates QSI points based on the itineraries they offer. The carrier’s share of total QSI points on the route is then used to estimate its likely share of demand.