There is a difference between " theoretical " strata and " real " or " effective strata. ".
A stratum is the crossing of all the stratification variables, which leads to 480 possible strata which are “theoretical” strata.
But in the reality of the pharmacy world, some strata do not exist, we do not carry out a selection of the strata, but relate this reality.
For example, we do not have a pharmacy with a turnover greater than 3M € in pharmacies in rural areas in Ile-de-France.
Only the “observed” or “effective” strata are kept, ie 132.
But the stratification model is adaptive , in the sense that if a new stratum appears or disappears, the model automatically adapts to take into account the number of “effective” strata.