The term "Replicates" refers to a sampling scheme designed to use as little sample as possible. The idea is to restrict the number of active sample in the field at any time. By active sample, we mean cases that have been used and are still alive (i.e. cases that are in a call-back status).
Replicate control over active sample in any chosen stratum is achieved by assigning it a quota and the Half-open status, and making sure that the Replicates option is activated.
To use the replicates feature, the steps are as follows:
In the Quotas tab, create strata for groups of sample over which you wish to apply replicates control.
Assign "quotas" to these strata. In this case, however, each quota represents the maximum number of active cases allowed in the stratum.
Apply the Half-open status to each of these strata.
Select the Replicates check box. This will change the rules applied to all of the Half-open strata. Rather than restrict the number of active interviews in progress (as for Half-open strata), the program will count and restrict the number of active cases in these strata.
Make sure that quotas are Active.
The number of active cases in each Half-open stratum (when the Replicates feature is selected) is restricted to the target "quota" minus the current number of completes for that stratum.
Notes:
Any stratum will switch to Closed when its quota is reached.
The Half-open status is equivalent to the Closed status if the stratum's quota is 0.
You cannot simultaneously control on the basis of both Half-open and Replicates rules in the same project.
For each stratum, the counter of active cases is increased when a case is called for the first time.
For each stratum, the counter of active cases is decreased whenever an interview is terminated without a call-back (completed or "dead" case).
When using the Replicates option, the on-line counter shows the number of active cases in the stratum.