The Strata and Quotas definition page allows you to manage subsets of the sample and to open or close access to any stratum or subset. It also allows you to apply quotas or ceilings to control the maximum number of completed interviews by stratum, and the rate at which they are attained.
Note: An interview is considered to be completed when it has reached the Completion question. See Design (Questionnaire Designer).
The term stratum (sometimes known as a quota cell) is used to refer to a subset of cases that conform to defined criteria. A quota is a maximum frequency or ceiling which can be applied to completed interviews in a stratum. Strata frequencies are computed and updated dynamically whenever the interviews are completed.
The Quotas page may be used for six different purposes:
To supervise a set of strata frequencies, or subsets of the sample, without actually affecting the field. This is done through inactive quotas.
To impose effective ceilings on strata. This is done through active quotas. In this mode, an interview is automatically interrupted as soon as it is detected as belonging to a stratum whose quota has been reached. In the case of imported sample, cases belonging to such strata are suspended from the field.
In the case of imported sample, or data captured in a previous interview, to control at will the release of calls to cases (respondents) belonging to any specific stratum. This is done through the open/half-open/closed switches.
To balance the release of sample across several strata through the use of Weights together with the Smoothing function.
To control the release of cases by time zone or other schedules.
To control (match) the release of sample subsets to nominated sets of interviewers. This can be done in one of two ways using either the Groups or the Roles sample assignment mode.
First, you must specify a set of criteria or strata, upon which sample control or quotas are to be applied; these strata do not have to be mutually exclusive. Usually strata are created using the Definition Wizard which can create many strata with one command. You can also create, specify and edit the criteria for each stratum individually in the Quota table itself; and you can use a combination of these two methods. The strata/quota definitions are stored in one of the project's database tables.
Note: The Command Center prevents any modifications to strata definitions while a project is active. These include: addition, insertion or deletion of strata, modifications to the criteria that define them; the Tools>Calculate command is also inactivated while the project is active.
Once the strata have been defined, you may then use the Quotas page to:
Specify the desired frequency for any stratum or for all completed interviews
Close, half-close, or open any stratum
Assign weights or roles to any stratum
Activate or de-activate quotas.
The Quotas page may be used at any time during the field, without risk.
Note: Strata can also be updated in batch mode. The Quotas module can also be used to view the status of the strata, and to modify their status or the quotas that apply to them.
If quotas are active, any stratum whose frequency has reached its specified quota is automatically closed (that is, the open/half-open/closed switch is set to Closed). If quotas are inactive, you may monitor the progress of quota attainment without actually affecting the field.