Interline Sample Accounting
In response to growth in the volume of interline transactions and the high cost of skilled staff, many airlines have adopted sampling techniques for the interline billing of other airlines' passenger tickets.
Sampling is based on the fact that characteristics of a population (universe) can be determined by an exact evaluation of a percentage or fixed number (sample) of that universe, picked at random.
By applying these scientific principles of random sampling to passenger billings, an airline need only evaluate a small number (sample) of total flight coupons (universe) to calculate the total value to a controlled and acceptable degree of accuracy.
Signatories to the Sampling Agreement (pdf)