Computational strata (for variance estimation)

In the cases where a country stratifies the sample by (for example) size class (using the standard output), and within each size class, the country uses systematic sampling by ordering the holdings by UAA, then Eurostat defines the "computational strata" by pairing the holdings considering their order (by UAA) within each original strata constructed by size class, ensuring that each "computational stratum" has at least two holdings. The relation between original strata and 'computational' strata is one to many. The "computational strata" are recorded in a dataset field, additionally to the original strata field.