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Flashcards in Biostats Deck (11)
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1
Q

Equation for Sensitivity and Specificity

A

Sensitivity = true positive / (true positive + false negative)

Specificity = true negative / (true negative + false positive)

2
Q

PPV and NPV

A

Both change based on prevalence of disease in population

PPV (inc if higher prevalence) = if positive test, how likely is it that you have the disease?

NPV (inc if lower prevalence) = if negative test, how likely is it that you don’t have the disease

3
Q

Absolute Risk v. Relative Risk

A

Absolute risk is the #1 who experience the risk / total # people

Relative risk is risk in those w/ X minus risk of those w/o X

4
Q

NNH and NNT

A

NNH = 1 / AR

NNT = 1/ ARR

5
Q

If someone performs at 1 ST above mean, what percentile are they in?

A

84th (68 + 13.5 + 2.5)

6
Q

How do you double the precision of a test?

A

Increase the sample size by 4

Because standard error (measure of precision) is std deviation divided by the square root of N

7
Q

Cohort v. Case Control Study

A

Cohort = prospective; look at those with and without exposure then see if they develop disease (MEASURE RELATIVE RISK)

Case Control = retrospective; start with those with and without disease and see who had exposure in the past (MEASURE ODDS RATIO)

8
Q

Selection Bias

A

Having sicker patients in placebo group

9
Q

Bergson Bias

A

Using hospitalized patients in a study instead of general population

10
Q

Lead-Time Bias

A

Interpret earlier detection of a disease (screening) as an increase in survival

11
Q

Type I and II Error

A

Type I = alpha = false positive (reject null hypothesis when you should not)

Type II = beta = false negative (should reject the null but do not)