Only want a survey to get sent on a configured frequency.
When wanting to send survey notifications on a specific frequency the Incident business rule 'Send Survey upon Incident Closure' should be disabled.
Instead a workflow should be created if it does not already exist that triggers on update of Status to specific value e.g. 'Closed' and the 'SendSurveyNotification' flag is set to "true" which is controlled by editing business rule on Incident object.
'SendSurveyNotification' logical field will only get set to true when the result of IncidentNumber divided by the 'IncidentSurveyFreq' global constant is a whole number, no remainder e.g. 'IncidentSurveyFreq' = 5 will send 2 surveys in every 10 sequential IncidentNumbers.