2.6 Screenings in Medicine Flashcards
What are 2 questions you should ask your physician when a medical screening test is recommended?
- How accurate is the test. 2. How confident will you be in your prediction of whether i do or dont have disease
What are the 4 screening outcomes?
True positive. True Negative. False Positive. False negative.
What does a True positive mean?
Test reports positive and the presence of disease does exist.
What does a True negative mean?
Test reports negative and the presence of disease doesnt exist.
What does a False positive mean?
Test screams positive but pts doesnt actually have disease.
What does a False Negative mean?
Test reports no disease but pt does have disease
What two terms describe the accuracy of a Test result?
Sensitivity and specificity.
What does sensitivity mean?
How well a test can detect presence of disease when in fact disease is present.
How would you calc sensitivity?
True positives / ( All diseased) x 100%
What is specificity?
How well a test can detect absence of disease when the disease is absent.
How would you calc specificity?
True negatives / (all not diseased) x 100%
What two terms describe how confident the doctor will be about predicting if the pt will have disease or not?
Positive Predictive Value and Negative Predictive Value.
What does the Positive Predictive Value (PPV) show?
How accurately a positive test predicts the presence of disease.
How do you calc PPV?
True positives / (All positive tests) x 100%
What does the Negative Predictive Value (NPV) show?
How accurately a negative test predicts the absence of disease.
How does one calc NPV?
True Negatives / (all Negative Tests) x 100%
What is Diagnostic Accuracy (DA)?
Proportion of total screenings that a pt is correctly identified as either having a disease (True positive) or not having a disease (True negative) with either a positive or negative test
How do you calc DA/DP?
(True Positive + True negative) / (All patients) + 100%
What are LRs?
Likelihood ratios, division on 2 numbers. Simple ppl with disease in numerator/ppl who dont have disease.
What is a LR+?
Probability of a positive test in the presense of disease / probability of a positive test in the absence of disease
How do you calc LR+?
Sensitivity / (1-specificity). Which is [A/(A+C)]/ [B/( B+D)]
What is LR-?
Probability of a negative test in the presence of disease / probability of a negative test in the absence of disease.
How would you Calc LR-?
(1-sensitivity)/Specificity. Which is [C/(A+C) / [D/ (B+D)]
What should the test show for LR+ so its significant?
Bigger than 10
What should the test show for LR- to so its significant?
Less than .1
What does validity mean?
Ability to accurately discern between those that do and dont have disease
What does reliability mean?
Ability of a test to give the same result on repeated uses.
True or False? A valid test is always reliable but a reliable test is not always valid.
True
