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Screening Tests, Reliability & Validity
Terms in this set (13)
General definition: measuring specific characteristics of individuals, usually for the purposes of classifying individuals into two categories:
Screening in Clinical Medicine
Testing to detect a disease (or risk factors for a disease) in a person who has no known signs or symptoms.
- Patients are asymptomatic: They don't know they have it
- Patients will have better outcomes(usually through therapeutic means) if the disease is detected before symptoms arise
# of Purposes of Screening Tests
Purpose #1 of Screening Tests
Primary prevention: preventing disease from occurring
-identifying risk factors for a disease so that its occurrence can be prevented by intervening on the risk factor
-cholesterol and blood pressure screening to prevent CVD
Purpose #2 of Screening Tests
Secondary prevention: reducing the impact of a disease that is already present
-identifying a disease at an early stage so that the course (natural history) of the disease can be altered through intervention
-Mammography or Pap smear to detect early breast CA or cervical CA
Reliability of a Screening Test
The ability of a measuring instrument to give consistent results on repeated trials...which is also referred to as "precision"
-"If I conduct this test 100 times, how many times out of 100 will the results be identical?"
Validity of a Screening Test
The ability of the measuring instrument to give a TRUE measure of the entity being measured
- Also referred to as "accuracy"
-"If I conduct this test 100 times, how many times out of 100 will the test give me the TRUE/CORRECT result?"
Reliability vs. Validity
-A test is valid if it measures what it is supposed to measure.
-- Ex. If the results of the personality test claimed that a very shy person was, in fact, outgoing, the test would be invalid.
------Reliability and validity are independent of each other. A measurement may be valid but not reliable, or reliable but not valid.-------
-The ability of the test to correctly identify all of the screened individuals who actually have the disease
-"Out of all of those individuals who ACTUALLY have the disease, the screening test correctly identified 98% of them."
The ability of the test to identify only non-diseased individuals who actually do not have the disease
-"Out of all those individuals who actually DID NOT have the disease, the screening test correctly identified 94% of them."
Positive Predictive Value (PPV)
The proportion of individuals screened positive by the screening test who actually have the disease
-"Out of all of those individuals who screened positive, the screening test correctly identified 88% of them."
-"Out of all of those individual who screened positive, 88% of them actually had the disease."
Negative Predictive Value (NPV
The proportion of individuals screened negative by the screening test who actually do NOT have the disease
-"Out of all of those individuals who screened negative, the screening test correctly identified 90% of them."
-"Out of all of those individual who screened negative, 90% of them actually did NOT have the disease."
Characteristics of a Disease that is a Good Candidate for a Screening Test
-Important health problem as measured by its severity, its frequency or both
-Effective treatment should exist—one capable of reducing morbidity and/or mortality
-Persons screened have access to follow-up facilities for diagnosis and treatment
-Treatment is known to be more effective if initiated early—in the pre-symptomatic stage rather than in the symptomatic stage
-"Suitable" screening testis available
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