Requirements for examination techniques

Investigative Techniques
Examination techniques are used to search for patients in the population.
 * 1) Individual detection - every examination of a person who sought medical help for any reason.
 * 2) Preventive inspection.
 * 3) Screening - search for at-risk or sick persons in the early or subclinical phase of the disease in a population of apparently healthy people using an appropriately chosen and simple screening test (clinical, laboratory, etc.). It is desirable that the screening test be highly sensitive and highly specific and the entire screening be truly beneficial.

Simple screening tests - questionnaires, X-ray examination, blood tests, EKG etc., or a combination thereof.

Multiple screening (multiple) – a set of tests to search for a greater number of diseases at the same time.

If we want to evaluate the quality of the used dg. test when searching for patients with a given diagnosis, it is best to organize the data into a four-field table:

Sensitivity
Sensitivity is the probability of a positive finding in a sick person 'a/(a+c).

Specificity
Specificity is the probability of a negative finding in a healthy person 'd/(b+d).

False positive

 * A positive result even in healthy people, its measure is the relative frequency of 'b/(b+d).

False negative

 * A sick person has a negative test result, its measure is the relative frequency of c/(a+c).

Predictive value of a positive test

 * Probability that a person is really sick when the test is positive 'a/(a+b).

Predictive value of a negative test

 * Probability that a person does not have the observed disease with a negative result of the 'd/(c+d) test.

Screening Test Accuracy

 * Indicates the probability that the test gives correct results in the screened population. We estimate it as (a + d)/n.

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