There are situations in which there is a need to regulate or balance the rate at which a group of strata are filled during the course of the field operation. To achieve this, you may assign a probability or weight to any stratum, in which case the system will dispatch the next respondent from a stratum randomly selected according to the assigned weights. To balance the rate of quota attainment, you may further specify that the program calculate and override the weights (smoothing). We recommend, though it is not mandatory, that weights be assigned only to mutually exclusive strata.
To assign a weight, enter a number greater than 0 in each stratum concerned. The probability that a stratum will be chosen is: weight of the stratum / sum of the weights.
The weight of a Closed stratum is automatically set to zero. Similarly, the weight of a stratum whose quota has been filled also has a value of zero when quotas are active.
To switch to automatic weight calculation mode, use the Smooth check box. The weight assigned to stratum (i) will be: (quota(i)-frequency(i)) / sum of (quotas - frequencies)
Negative values are treated as zeros. Automatic weights are calculated only for strata which have been manually assigned a positive weight. These weights are calculated continuously.
To return to using manually assigned weights, simply un-check the Smoothing option (Strata/Quotas page).
Within a stratum, cases are picked in the same sequence as they are ordered in the file. Rules relating to other strata remain applicable.
If no case is available in the chosen stratum (exhausted sample, or if all cases belong to other closed strata), the system will ignore weights and dispatch the next available case in the sample (for the current case only).
Note: Weighting applies both to cases which are unused and those which are in soft call-back state.