At each patient contact, ask the number of days with symptoms in the previous two weeks.  Subtract that number from 14 to get the number of symptom-free days for the patient in the previous two weeks.  (Sum the symptom-free days over all patients. Divide the sum by the number of patients in the registry.)

Greater than 10 days.

On the last workday of each month, search flow sheets, charts or the registry to find the patients who had a severity assessment at last contact.  Use the estimate of symptom-free days provided at this contact.  Exclude patients who have not yet been entered into the registry.