Frequency is the number and spacing of selection periods during the program period. Typical frequencies are monthly, weekly, quarterly, or daily. Other frequencies are possible and sometimes helpful. A high frequency of selections, i.e. daily, results in a very high level of deterrence. However, it also tends to be more difficult to administer. As a general rule for establishing deterrence, you should use the highest frequency possible given your administrative capabilities. For example, if all of your pool members are located at a single facility with on-site collection capabilities, then weekly, or even daily selections are possible. But if the same number of people are spread out over a large geographic area with diverse work schedules, monthly or quarterly selections may be more appropriate.
The key factor that helps determine frequency is the ability to locate, notify, and collect a sample from the individual selected for testing. That ability is driven by your communication abilities, management practices, geographical structure, and collector arrangements. Of course, all of these are related to the cost of the testing program.