Ans. (a) Diagnosed cases under treatment* Iceberg Phenomenon of disease: Disease in a community may be compared to an iceberg- Floating tip is what physician sees in community, i.e., clinical cases- Vast submerged portion of iceberg represents hidden mass of disease i.e., latent, inapparent, pre-symptomatic and undiagnosed cases and carriers in community- Line of demarcation (water surface): Is between apparent and inapparent infections- Water surrounding iceberg: Healthy populationALSO REMEMBER* 'Epidemiologist is concerned with Hidden portion of iceberg' whereas Clinician is concerned with Tip of iceberg* 'Screening is done for Hidden portion of Iceberg' whereas diagnosis is done for tip of iceberg* Iceberg phenomenon of disease is not shown by:- Rabies- Tetanus- Measles- Rubella