Lecture 4 Flashcards
Diagnostic
Used to determine the presence or absence of disease when a subject shows signs or has symptoms. Occurs after a screening test.
Ex: Covid tests
Sign
Something that can be seen, measured, or observed. This is objective
Symptom
A condition that is perceived or felt by an individual. This is subjective.
Screening
Used to identify asymptomatic individuals who are at risk for a disease.
Ex: Colonoscopies, Ocular Pressures, Mammography, Lipid tests
U.S Preventive Services Task Force
An independent panel of non-Federal experts in prevention and evidence-based medicine and is composed of primary care providers. They come up with the recommendation statements about screening tests.
Reference Range (Interval)
Established by testing a large number of health people and observing what appears to be “normal” for them.
Why do we have diagnostic and screening tests?
It’s important to understand how a disease is developed and transmitted. (So we know how to stop it) It’s also important to distinguish between people that do have the disease and those that do not. (So we know what are lifestyle risks that are attributing to it). This is all in order to provide effective healthcare.
How good is the test at identifying populations of people with the disease?
The quality of a test must be good in order for us to provide accurate diagnostics. We don’t want false positive or false negative cases. The goal is to get as many true positive or as many true negative cases.
What is the logic behind screening?
Screening is built on the idea of reference ranges. A reference range is established by testing a large number of healthy people and observing what appears to be “normal” for them. The results that come from these healthy populations are used to create normal values with standard deviations. For example blood pressure, weight, etc. By screening people we can see where they fit on the scale compared to our reference range values.
What is the validity of a screening test?
The ability of a test to distinguish those who have the disease and those that do not. This is sensitivity and specificity.
Sensitivity
The ability of the test to correctly identify those who have the disease. This is the true positive group.
Specificity
The ability of the test to correctly identify those who do not have the disease. This is the true negative group.
What is wrong with the results of the dichotomous test?
The test results in identifying people as True Positives, False Positives, True Negatives, and False Negatives. This means the test is mis-identifying people who have the disease/people who are disease free.
False Positive situations
These are people who tested positive for the disease initially and must come back for more intensive testing which can be expensive, and anxiety inducing because this person thinks they may have the disease.
False Negative situations
These are people who tested negative for a disease but actually have it. This is dangerous because the disease can be life-threating. It’s also more expensive to treat a disease in the later stages. Importance of a false negative depends on nature and severity of the disease being screened for, effectiveness of available intervention measures, and whether effectiveness of treatment was greater had it been administered in the early history of the disease.
How do we test continuous variables?
In situations like measuring blood pressure we can’t use labels such as disease and disease free. Instead we must use cutoff values. These are high and low values that can be identified as a “positive” result or a “negative” result.
What is the point of the cut-off value?
The point of the cut-off value is to establish those that are “positive” for a condition so they can come back for further testing and those that are “negative”.
Choosing a high cut-off value
A high cut off value will correctly identify a lot of negative cases. It will identify only a few positive cases. Specificity is high and sensitivity is low. Risk of missing positive cases!
A lot of TN
Choosing a low cut off value
A low cut off value will correctly identify a lot of positive cases. It will identify only a few negative cases. This means even some negative cases are going to be identified as positive. Sensitivity is high and specificity is low. Results in too many “positive” cases, probably misdiagnosed with FP’s/
A lot of FP’s and
What is the importance of reliability?
Reliability is good to have because you want to be able to replicate the results over and over again. This is a good indicator of a test being accurate.
Intra-subject variation
This is when results coming from an individual vary due to environment and actions that a person has done that day. Think food eaten, stress levels throughout day, amount of sleep, alcohol usage.
Intra-observer variation
One observer makes multiple observations of the same thing at different times. This is used to test medical professionals to ensure they make proper diagnoses. They are re-tested on old diagnoses.
Inter-observer variation
Variation between more than one observer. To what degree do they agree or disagree?
Why do we measure % agreement between two observers?
It’s a way to measure the quality of their observations. It’s important for two doctors or two nurses to agree with one another in order to provide quality of care.
How to fix the problem of false positives?
Conduct further testing to see if the individual actually has the disease.
Sequential Testing
This is two-stage testing. The first test is low-cost, less invasive, and less uncomfortable. All that tested positive are brought back for a second round of testing that has a higher sensitivity/specificity. Can be more invasive, expensive, and uncomfortable.
Simultaneous Testing
We use 2 tests at the same time to screen for disease. Sensitivity and specificity of both tests differs.
Sequential Testing Benefits
When we re-test whoever tested positive on the initial test there is a loss in net sensitivity and a gain in net specificity.
