UNDERSTANDING THE QUALITY OF DATA IN CLINICAL MEDICINE Flashcards
requires constant collection, evaluation, analysis, and use of quantitative and qualitative data
Clinical medicine
is used for diagnosis, prognosis, and choosing and evaluating treatments
Data
o Mistakes in the diagnosis and treatment of patients
o Mistakes due to clear negligence
Error
First and primary goal of data collection and analysis
Promote accuracy and precision
Close to true value
Accuracy
Ability of a measurement to be correct on the average
Accuracy
Precision is also known as
Reproducibility, reliability, or agreement
Ability of a test to give the same result or a similar result with repeated measurement of the same factor
Precision
MEASURES OF RELIABILITY
Overall percent agreement
Kappa test ratio
Kappa test ratio is also known as
Cohen’s Kappa
• Common way to measure agreement
OVERALL PERCENT AGREEMENT (OPA)
Percent agreement formula
a+d/
a+b+c+d x 100
OPA when there are just 2 people observing
PERCENT AGREEMENT (PAIRED OBSERVATIONS)
OPA when there’s a lot of variables invloved
OVERALL PERCENT AGREEMENT (MULTIPLE VARIABLES)
Measures the extent to which agreement exceeds that expected by chance
KAPPA TEST RATIO
• How much better is the agreement between two observers’ readings than would be expected by chance alone?
KAPPA TEST RATIO
• What is the most that the two observers could have improved their agreement over the agreement that would be expected by chance alone?
KAPPA TEST RATIO
: happens when the information errors differ between groups
Differential error
: happens when the information is incorrect, but is the same across groups
Nondifferential error
refers to any systematic error that may occur during the collection of baseline or follow-up data
Measurement bias
Variability and unpredictability
results in lack of precision
When data have only _______, some observations are too high and some are too low
Random error
Intraobserver variability or
Within the observers
Amount of variation between the results obtained by one observer examining the same results more than once
Example: same clinician takes successive blood pressure on the same patient
Intraobserver variability
Amount of variation between the results obtained by 2 or more observers examining the same material
Interobserver variability
Ability of a test to distinguish between WHO HAS a disease and WHO DOES NOT
Validity
is performed as a preventative measure – to detect a potential health problem or disease in someone that doesn’t yet have signs or symptoms
screening tests
able to correctly identify who has the disease
Sensitivity
– correctly identifies who does not have the disease
Specificity
Have the disease and test positive
True Positive (TP)
Do not have the disease but test positive
False Positive (FP)
Have the disease but test negative
False Negative (FN)
Do not have the disease and test negative
True Negative (TN)
Sensitivity formula
TP/
TP + FN
Specificity formula
TN/
TN + FP
How about tests with continuous variables?
Such as blood pressure or blood glucose levels
There is no “positive” or “negative” result
Cutoff points
The _______ determines how many subjects will be considered as having the disease
cut-point
The cut-point that identifies more true negatives will also identify more ____________
False negatives
The cut-point that identifies more true positives will also identify more ____________
False negatives
• When two or more tests are conducted in parallel simultaneously )
• Disease positives are identified as those who test positive by either one test or by both tests
SIMULTANEOUS TESTING
• After the first (screening) test was conducted, those who tested positive were brought back for the second test to further reduce false positives
SEQUENTIAL (TWO-STAGE) TESTING
_: less expensive, less invasive or less uncomfortable
First test/ screening
____________: more expensive, more invasive or more uncomfortable
Second test/ confirmatory
A ____________, which is used to rule out a diagnosis, should have a high degree of sensitivity.
screening test
A _____________, which is used to rule in a diagnosis, should have a high degree of specificity.
confirmatory test
/o If something is said to be true when it is actually false
Type 1 terror
false-positive error
Alpha error
o If something is said to be false when it is actually true
Type II
False-positive error
Beta error
o Reliably finding a disease when it is present
o Avoids false negative results
Sensitivity
Reliably excluding a disease when it is absent
Avoids false positive results
Specificity
• Describe the probability of having actual disease given the results of a test
PREDICTIVE VALUES
Indicates what proportion of the subjects with positive test results actually have the disease
Positive Predictive Value (PPV )
Indicates what proportion of the subjects with negative test results actually do not have the disease
Negative Predictive Value (NPV)
• “RULE IN DISEASE”
• Ratio of the sensitivity of a test to the false-positive error rate of the test
LIKELIHOOD RATIO POSITIVE (LR+)
• “RULE OUT DISEASE”
• Ratio of the false-negative error rate divided by the specifici
LIKELIHOOD RATIO NEGATIVE (LR-)
______ and _______ assess how good a test is at diagnosis of disease while ____________ predicts the risk of disease for a particular test.
Sensitivity and specificity/ likelihood ratio
_________ and _________ both predict risk of disease, but, unlike predictive value which depends on the prevalence of the disease, likelihood ratio does not.
Predictive value and likelihood
