Exam 6 - EpiStats

Question 1

Incidence

Answer 1

• How many new contractions of disease

- How many are coming in

Question 2

Prevalence

Answer 2

• The % of population who have the disease

Question 3

Recurrence

Answer 3

• Those who get better and then get sick again

Question 4

Mortality

Answer 4

• Death

- Those leaving the prevalence pool

Question 5

P-value

Answer 5

• How likely these results would occur strictly by chance
• If calculated p-value is less than picked level…we reject the null hypothesis
• Example: p-value is 0.05… we would expect this result 5% of the time by chance alone

Question 6

EDAC

Answer 6

Emboli Detection and Classification

Question 7

How to set up grid

Answer 7

• Disease on top
• Test results on side
• Yes then No
• Sensitivity and Specificity on bottom (left to right)
• PPV and NPV on Right side (top to bottom)

Question 8

TP

Answer 8

• true positive

- have disease and test positive for it

Question 9

TN

Answer 9

• True negative

- Do not have disease and test negative for it

Question 10

FP

Answer 10

• False positive

- Don’t have disease but test positive for it

Question 11

FN

Answer 11

• False negative
• Do have disease but test negative for it
• WORST outcome

Question 12

Sensitivity

Answer 12

• Think positive
• % of those who are positive and test positive
• TP/(TP+FN)
• If high…. low chance of a FN
• Remain constant regardless of population
• High sensitivity = Good screening tests

Question 13

Specificity

Answer 13

• Think negative
• % of those who are negative and also test negative
• TN/(TN+FP)
• If high…. low chance of FP
• Remain constant regardless of population

Question 14

Type I error

Answer 14

• FP

Question 15

Type II error

Answer 15

• FN

Question 16

Ideal test conditions minimize what?

Answer 16

• Minimize the FN and FP

Question 17

PPV

Answer 17

• Positive predictive value
• TP/(TP+FP)
• % that there is disease in those who test positive for the disease
• measures the usefulness of a test
• can vary across populations
• HIGHLY dependent on prevalence

Question 18

NPV

Answer 18

• Negative predictive value
• TN/(TN/FN)
• % that no disease is present among those who have tested negative
• measures the usefulness of a test
• can vary across populations
• HIGHLY dependent on prevalence of disease

Question 19

CI

Answer 19

• Confidence Interval
• (1 - p value)
• Between 90-95% is standard in medicine ‘
• much higher in technology
• affected by smaller sample sizes
  - small sample sizes have wider, varying intervals

Question 20

How to calculate a CI

Answer 20

• Subtract sensitivity from unity (1)
• Multiply result by sensitivity
• Divide result # of tests
• Square Root the result to get “standard error”
• Multiply standard error by “normal distribution” (given)
• Sensitivity +/- this result equals your CI