Which of the following characteristics is not of much importance in a screening test
Ans. is 'd' i.e. High specificity All are important attributes of screening test but among them high specificity is less important as Park states - ''Screening test is not intended to be a diagnostic test. It is only an initial examination. Those who are found to have positive test results are referred to a physician for further diagnostic work-up & treatment. High specificity is a necessary attribute for a diagnostic test.Below are given the differences between screening and diagnostic tests. Screening testDiagnostic test1.Done on apparently healthy (asymptomatic)Done on those with indications or sick2.Applied to groupsApplied to single patients, all diseases are considered3.Test results are arbitrary and finalDiagnosis is not final but modified in light of new evidence, diagnosis is the sum of all evidence4.Based on one criterion or cut-off point (e.g., diabetes)Based on evaluation of a number of symptoms, signs and laboratory findings5.Less accurateMore accurate6.Less expensiveMore expensive7.Not a basis for treatmentUsed as a basis for treatment8.The initiative comes from the investigator or agency providing careThe initiative comes from a patient with a complaintCriteria for Screening test- acceptability- safety- repeatability- rapidity- validity- ease of administration- simplicity- low costScreening test must satisfy the criteria ofAcceptabilityConsidering that screening tests are applied on asymptomatic people in large numbers, a high rate of people cooperation is needed. Thus the tests should be acceptable to the people. In general, tests that are painful, discomforting or embarrassing (eg. rectal or vaginal examinations) are not likely to be acceptable to the population in mass campaigns.Repeatability (Precision or reproducibility)means that the test must give consistent results when repeated more than once on the same individual or material under the same conditions.Low costA screening should be inexpensive. As a screening test has to be applied on millions of people to identify a small percentage who have early disease or its precursors, an expensive test however good, cannot justify use of restricted financial resources that has to be used for further diagnostic workup and t/t of those screened on positives.High safety marginThis is an attribute of any test, whether diagnostic or screening. Moreover for screening as screening tests are to be applied on millions of asymptomatic people and any adverse effect would bring whole process into disrepute.ValidityIt expresses the ability of a test to separate or distinguish those who have the disease from those who do notValidity has two components - sensitivity & specificityAn ideal screening test should be both highly sensitive and highly specific. But this is seldom possible and a compromise has always to be made.
Low cost
High safety margin
High sensitivity
High specificity
Screening for Disease