88 - Stats Revision

Question 1

How can sensitivity/specificity be ascertained?

Answer 1

Compare performed test to ‘gold standard’ test.

Question 2

Positive predictive value

Answer 2

Of all positive tests, what proportion are truly positive

Question 3

Negative predictive value

Answer 3

Of all negative tests, what proportion are truly negative

Question 4

Measures of the accuracy of a test

Answer 4

Sensitivity and specificity (inherent to a test and are constant)

Question 5

What are PPV and NPV dependent on?

Answer 5

Sensitivity and specificity.

Prevalence of outcome.

Question 6

What can make PPV appear really low, even though specificity can be high?

Answer 6

If a disease is rare enough. The number of false positives can overwhelm the number of true positives, as the number of negative cases is so much higher than positive cases.

Question 7

What does PPV positively correlate with?

Answer 7

Underlying prevalence of disease

Question 8

What does the utility of a diagnostic test rely on?

Answer 8

The underlying prevalence of disease (because is related to PPV)

Question 9

When do you order diagnostic tests?

Answer 9

When there is a strong clinical suspicion of disease.

Because test relies on underlying prevalence of disease.

Question 10

When are diagnostic tests not used?

Answer 10

To screen for diseases.

Question 11

Who are targeted for screening tests?

Answer 11

Those with high risk of outcome of interest.

EG: Mammography on women over 50

Question 12

Why wouldn’t you use a diagnostic test to screen for disease?

Answer 12

Because the underlying prevalence of a disease that is screened for with a diagnostic test is low. This means that the PPV will be low, and the chance of a true positive result is overwhelmed by the chance of a false positive result.

Question 13

What is biostatistics concerned with, w/r/t samples?

Answer 13

The extent to which the study (sample) results reflect the ‘truth’