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11 Cards in this Set

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  • Back

Evaluating Diagnostic Tests - cause of over estimating accuracy

due to people not considering bias rate - the likelihood of the disease occuring in the population= pre test probibility = post test probibility

risk % of having a pos mamogram

if a woman has breast cancer she is 90% likely to have pos mamogram

woman without mamogram still has 7% liklihood of a pos reading

2x2 contigency table - diagram example mamogram

how to correct percentages to probability and calc sens and secificibility- Mamogram ex

Pre test probability = .008 (.8%)

Sensitivity (%correct positives)= .90 (90%)

Specifity (%correct negatives : 100-7)= .93 (93%)

Diagnostic Tests and SIgnal Detection Theory

Diagnostic test can maximise the num of correct hits/diagnosis by adopting a liberal response bias

This causes minimisation of false neg by increasing false pos as false neg are regarded as worse

however these false positives may lead to unecessary surgery and treatment

Risk of HIV given a positive screening

prob of someone with no known risk behaviour is .01%. if a person has HIV 99.98% chance test will be positive. 99.99% chance is someone doesnt have aids that itll come back neg

Prob that person with a positive test has aids ? 50%

How to Choose the best pass mark of your diagnostic test

ROC curve

-crucial if you want to pick a pass mark that would lead to best descrimination between people

Concussion- Mild brain injury and ROC curves

does adding a non-word memory rep task improve detection of current test of cog effects?

Ps were patients from hospital with and without concussions

It matters what we choose as a pass mark

ROC Curve

Reciever Operating Characteristic

Is a plot of Correct positive rate (sensitivity) versus false positive rate (1- specificity) where each point on the curve is a different pass mark for the test

As true positive rate increases with a change in pass mark,so does false positive rate - sensitivity increases but specificity decreasses

the more the line curves away from the diagonal the better the test is at discriminating people with disorder from controls. the area under the curve equated to the overall diagnostic accuracy of the test regardless of pass mark chosen.

where to find the best point for a passmark on ROC curve

the point on the curve where sensitivity and specifictiy are highest. this point macimises correct hits and misses and minimizers fasse pos and neg

still more of lecture you have not done