Quiz 3 - Validity And Stuff Flashcards
Test
Any clinical an examination, observation, or evaluation, used to determine health or disease outcomes, and potential exposures
Two types of tests
Screening tests and diagnostic tests
Screening tests
Used as a population approach to apparently healthy individuals to detect sub Clinical disease
provides early indication of pathological, disease,
example, colonoscopy, or Irvine assay
Diagnostic test
Used on sick individuals with clinical disease to confirm classify inform treatment, or provide a prognosis for a particular disease
Validity of a test
Ability to distinguish between who has a disease, and who does not
Subcategories of validity
Sensitivity and specificity
Sensitivity
Ability of a test to identify correctly those who have the disease
Specificity
The Bility of a test to identify correctly those who do not have a disease
Reliability of tests
Repeatability can the same test results be obtained/replicated if the test is repeated?
Regardless of sensitivity and specificity of a test, if the test value cannot be read, reproduced the value and usefulness of test is low
Validity on a curve
When the halfway point of the curve is near the true value
Reliability on a curve
After the test has been measured various times, the deviation
Gold standard test
When a test has perfect validity and all diagnoses are correct and there are no mis diagnosis
2 x 2 tables purpose
To evaluate performance of diagnostic tests to analyze the relationship between two variables, such as binary health and disease, outcome, and binary exposure
How to build 2 x 2 tables
Always put you outcome, (gold standard) health or disease statement on the top
put the test you’re going to evaluate on the sides
True positive
Cell A of 2 x 2 table
someone that is truly sick
False positive
Cell be not truly sick negative on the gold standard test positive on the new test
causes may be result of test cross reacting with similar disease, agent or marker due to previous vaccination or infection
False negative
Cell c
Maybe the result of testing to early in the course of disease before biological changes occurred or presence of test inhibiting substances example, immunocompromise person, unable to produce enough biomarker being tested
Diurnal variation
May cause false negatives if the timing of the test/biological cycle influencing what is being measured
Sensitivity equation
Sn = a / (a+c)
(Proportion of outcome positives given the test positive)
As a sensitivity increases the number of false negative decreases
Means were able to detect a disease if present
Specificity equation
Sp = d / (b+d)
Proportion of negative outcomes given they test negatively
As sp increases, the number of false positive decreases
Snout
If a test is highly sensitive, and you get a negative result, you can be confident in ruling the disease out
Ex. Cancer tests won’t say you don’t have cancer if you do
As sensitivity increases the number of false negative decreases
Spin
If a test is highly specific and you get a positive test result, you can be confident in ruling a disease in (as sp increases, number of false positives increases)
Ex. If treatment for disease is painful or dangerous we don’t want to give it to someone that doesn’t definitely have the disease
True prevalence
The true proportion of disease within the population
Usually determined by gold standard test
= (true positive, a) + (false negative, c) / (total pop., n)
Apparent prevalence
The observed proportion of disease within the population
Usually determined by results if new test being evaluated
= (true positive, a) + (false positive , b) / (total pop., n)
