Diagnostic Tests/Sensitivity/Specificity/ROC Flashcards
1
Q
Screening Tests
A
- Medical tests or procedure performed on members (subjects)
- Defined, asymptomatic population or population subgroup
- Assesses likelihood of their members having a particular disease
2
Q
Screening tests DON’T…
A
- diagnose the illness
- Testing positive usually requires further evaluation with diagnostic tests/procedures
3
Q
Planning a Screening Program
A
- Disease/condition being screened should be a major medical problem
- Acceptable treatment should be available for individuals with disease
- Access to health care facilities/follow-up services should be available
- Disease should have a recognized course with early to late stages
- Tests/procedures should be accepted to general population
- Natural history of disease should be understood
- Policies and procedures should be determined to know who needs further testing/treatment
- Process should be simple enough to encourage large groups to participate
- Screening should be an ongoing activity
4
Q
“Perfect” Diagnostic Test
A
- All individuals without disease give one uniform value
- All individuals with disease give a different, uniform value
- All test results coincide with being diseased or disease free
5
Q
Normal/”Reference” Range
A
- Not all values are the same in disease free individuals
- Disease free individuals will have a range of values (Reference Range)
- “Normal” misrepresents the range - distribution may not be normal and the individuals could be in range and not be healthy
6
Q
Reproducibility/Reliability of Test
A
- Ability to produce consistent results when repeated under same conditions
- Re-testing requires operator/observer to remain the same and blinded to results of 1st test
7
Q
Kappa
A
- K
- Index of agreement
8
Q
Precision
A
- Agreement of repeated measurements
- Range of results +/- SD
9
Q
Accuracy of Test
A
- Agreement of test values with true value
- Accuracy requires reliability or precision
- Results can be reliable without being accurate
- (T-) + (T+)/All
10
Q
Validity of Test Types
A
- Content validity - test represents what is trying to be measured
- Criterion Validity - Test results agree with other results measuring the same parameter
- Construct Validity - Real biological property being measured to explain why results vary among individuals
11
Q
Diagnostic Test Results
A
- Most often think or patients having or not having disease
- Nearly all disease processes are continuous
- Disease severity and number of symptoms tends to increase over time
- More difficult to diagnose early stages of disease while late stages are more distinct
12
Q
“The Gold Standard”
A
- Test whose results determine disease status
- Assumed to be 100% accurate/true
- Many diseases lack a test like this
- New tests are always compared to gold standard
- New drugs always compared to placebo control or current drug of choice (active control)
- Accuracy of new tests are always less or equal to gold standard
- New tests can outperform gold standards and become new gold standards
13
Q
Steps Determining Diagnostic Performance
A
- Choose gold standard test
- Perform gold standard test on a full spectrum of subjects
- Test all subjects with new diagnostic test
- Compare results of both tests in a 2x2 table
- Calculate the proportions of accurate and inaccurate results of the new test
14
Q
Prevalence + Diagnostics
A
- If proportion with disease is high, easy to diagnose a disease positive
- If proportion with disease is low, easy to diagnose a disease negative
- Surrogates for positive/negative disease diagnosis determine if patients will respond to drug therapy and likely drug therapy failures
15
Q
Reporting Prevalence
A
- Percentage
- Number of cases per a total number of people
