State model for partly undetected non-communicable diseases (NCDs)
  This article proposes an age-structured compartment model for irreversible diseases with a pre-clinical state of undiagnosed cases that precedes the diagnosis. The model is able to cope with mortality rates differing between the pre-clinical and the clinical state (differential mortality). Applicability is tested in a hypothetical disease with realistic incidence and mortality rates. 
Ralph Brinks
q-bio.PE