1. Screening - screening refers to the search for unrecognised disease or defect in apparently healthy person by the application of rapid Diagnostic test ,examination & procedures. The basic objective of screening is to facilitate an early diagnosis so that the prognosis can be improved.

2. Mass screening - when all members of a population are screened for disease it is called Mass screening. This is very costly.

3. High risk screening - it refers to the situation where test are offered only to those individuals who are at high risk of developing a specific disease. this make the screening process more focused and reduces the overall cost as a large number of people who have extremely minimal chances of developing a disease are not screened.

4. Criteria of screening for any disease -

- the condition should be an important public health problem.

- the natural history of the condition from the latent to manifest disease should be adequately understood.

- there should be a recognisable latent or asymptomatic stage of the disease during which identification will lead to improved prognosis or outcome.

- facilities for full Diagnostic workup and treatment should be available.

- they should be a suitable test available.

- case finding should be a continuous process.

- the test should be acceptable both to the public as well as the professional.

5. Specificity - it refers to the proportion of the normal individual who are correctly labelled as non diseased by the scanning test. Test with high specificity will only give a few false positives. 

6. Sensitivity- this refers to the proportion of truly diseased individual in the population who have been correctly identified as disease by the screening tests. Test with high sensitivity gives only a few false negatives.