Diagnosis

Question 1

reference standar

Answer 1

a test with established or widely accepted acucracy for determining a diagnosis.

• we compare a new test to this reference standard.

Question 2

selection bias

Answer 2

inclusionof specitic patients that might affect the way the data affects/presents.

ex/ including people who only have had large strokes to see if CT is diagnostic vs people with different types of strokes

Question 3

misclassification bias

Answer 3

inexperienced reasers who might be reading the test results wrong (ex/ selecting something as positive when really they tested negative.

Question 4

unrepreseentative sample selection due to sampling/selection bias may result in ___ ____

Answer 4

spectrum bias

Question 5

what is spectrum bias

Answer 5

when the study sample is not representative of the popualtion, and thus the accuracy of diagnostic test is assessed in population that does not meet this ideal. the diagnostic test doesn’t perform well in the population because the sample was not representative.

Question 6

pretest probability

Answer 6

probability of target condition being present before results of the diagnostic test are known

ALSO KNOWN AS DISEASE PREVALENCE

Question 7

the Probability of target condition being present
after results of diagnostic test are known is known as the -__ probability

Answer 7

post test probabiltiy

Question 8

A person is wanting to see if they can diagnose strokes only by CT. They choose to have their reference standard as “ all clinical imaging– the CT and MRI put together”. what is wrong with this reference standard?

Answer 8

there is INCORPORATION BIAS: there is a lack of independence from the reference standard and the investigative processes

Question 9

how does incorporation bias change the accuracy of your diagnostic tool

Answer 9

there will beinflated accuracy

Question 10

what is expectation bias?

Answer 10

in clinical practice; a clinicians assessment may be influenced by previous knowledge of the presence or absence of a disorder

in data collection; an interviewer has information that influences his or her expectation of finding the exposure or outcome

Question 11

what is verification bias

Answer 11

also called workup bias or differential verification bias

• occurs when test results influence choice of reference standard and assessment of test results is biased.
• ex/ test- postive patients undergo an invasive test to establish diagnosis; tst- negative patients undergo longterm follow up instead. this causes inflated accuracy because the people with the positive tests are getting the reference tst but we are not using the reference test on the negative– thereofre all the postiive tests will have a correlated positive reference standard.

Question 12

two measures of accuracy in a diagnostic test

Answer 12

sensitivity or specifcitiy

Question 13

two measures of prediction in diagnostic test

Answer 13

PPV and NPV

Question 14

what is a measurement of diagnostic probability for a diagnostic test?

Answer 14

likelihood ratio

Question 15

sensitivity

Answer 15

proportion of people with the disease that are correctly detected by the test. TN>>>>FN therefore, any test negative is likely to be a atrue negative.

Question 16

specificty

Answer 16

proportion of people who are free of a designated disoede who are so identified by the test– if the test is highly specific, if it is positive, it is probably a true positive.

Question 17

a highly sensitive test can rule ____ a disease, and a highly specifci test can rule ____ a disase

Answer 17

sensitive: can rule OUT a disease. if a highly sensitive test is negative, it has a high likelihood of being a true negative because the rate of false negatives are very low.

specific test: can rule IN a disease. if a highly specific test is positive, it has a very high likelihood of being a true postivie because the rate of false positives are very low. ( B/(B+D)

Question 18

positive predictive value

Answer 18

the proportion of people who test positive that actually have the disease of interest.

Question 19

NPV

Answer 19

the proportion of people who test negative that are actually free of the disease of interest.