Epidemiology/Biostats

Question 0

Purpose of case-control study

Answer 0

Compares a group of people with disease to a group without disease–What happened?

Gives Odds Ratio

Question 1

Purpose of Cross-sectional study

Answer 1

Assesses frequency of disease ata a particular point in time. Asks: What is happening?

Question 2

Cohort Study

Answer 2

Compare a group with a given exposure/risk factor to a group without such exposure

Question 3

What is the purpose of a cohort study?

Answer 3

It compares a group with a given exposure of risk factor to a group without such exposure to see if the exposure INCREASES the likelihood of diseas–Who will develop the disease?

Relative risk (RR)

Question 4

Twin concordance study

Answer 4

Compares frequency with which both monozygotic twin or both dizygotic twins develop same disease

Measures heritabilty and influence of environmental factor

Question 5

Define sensitivity (true-positiv rate)

Answer 5

Its the proportion of all people with a disease who test positive, or, its the probability that a test detects disease when the disease is present.

Question 6

What does it mean when sensitivity (true-positive rate) is 100%?

Answer 6

A value approaching 100% is desirable for RULING OUT disease and indicates a LOW FALSE-NEGATIVE RATE.

High sensitivity test used for screening in diseases with low prevalence.

Question 7

What is the equation for sensitivity (true-positive rate)?

Answer 7

True-positive rate = (TP)/(TP+FN)

TPr = 1 - FNr

Question 8

What is the definition for specificity (true-negative rate)?

Answer 8

Its the proportion of all people without disease who test negative, or the probability that a test indicates non-disease when the disease is absent.

Question 9

What does it mean when specificity (true-negative rate) is 100%?

Answer 9

A value approaching 100% is desirable for RULING IN a disease and indicates a LOW FALSE-POSITIVE RATE.

High specificity test used for confirmation after a positive screening test.

If specificity is 100%, all positives must be TPs.

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Question 10

What is the equation for specificity (true-negative rate)?

Answer 10

TNr = (TP)/(TN+FP)
TNr = 1 - (false-positive rate)

Question 11

What is the positive predictive value (PPV)?

Answer 11

It’s the proportion of positive test results that are true positive, or, the probability that a person ACTUALLY has the disease given a positive test result

Question 12

What’s the equation for positive predictive value (PPV)?

Answer 12

PPV = (TP)/(TP+FP)

Question 13

PPV is proportional to _________.

Answer 13

Prevalence (or) pretest probability

Question 14

What is the definition of a negative predictive value (NPV)?

Answer 14

It is the proportion of negative test results that are true negative, or, the probability that a person ACTUALLY is disease FREE given a negative test result.

Question 15

What is the equation for negative predictive value (NPV)?

Answer 15

NPV = (TP)/(TP+FP)

Question 16

NPV varies _________ with prevalence or pretest probability.

Answer 16

inversely

Question 17

Equation for incidence rate

Answer 17

Incidence rate = (# of new cases in a specified time period)/(population at rate during same time period)

Question 18

Equation for prevalence

Answer 18

Prevalence = (# of existing cases)/(population at risk)

Prevalence looks at all current cases

Question 19

Prevalence __(,=)__ incidence for chronic diseases

Answer 19

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Question 20

Odds ratio (OR) are typically used in ________ studies.

Answer 20

case-controlled

Question 21

Define Odds ratio (OR); give its equation

Answer 21

It is the odds that the group with the disease (cases) was exposed to a risk factor (a/c) divided by the odds that the group without the disease (control) was exposed (b/d)

Question 22

What is the equation for Odds Ratio?

Answer 22

OR = (a/c)/(b/d) = ad/bc

Question 23

Define relative risk (RR)

Answer 23

It’s the risk of developing disease in the exposed group divided by risk in the unexposed group

(eg - if 21% of smokers devlop lunch cancer vs 1% of nonsmokers, RR = 21/1 = 21)

Question 24

What’s the equation for relative risk (RR)?

Answer 24

RR = (a/[a+b])/(c/[c+d})

Question 25

Define relative risk reduction and give its equation

Answer 25

Its the proportion of risk reduction attrivutable to the intervention as compared to a control.

RRR = 1 - RR

(eg - if 2% of patients who receive a flu shot develop flu, while 8% of unvaccinated patients develop the flu, then RR = 2/8 = 0.25, and RRR = 1 - RR = 0.75)

Question 26

Define attributable risk

Answer 26

Its the difference in risk between expoed and unexposed groups, or the proportion of disease occurrences that are attributable to the exposure

(g - if risk of lung cancer in smokers is 21% and risk in nonsmokers is 1%, then 20% (or .20) of the 21% risk of lunch cancer in smokers is attributable to smoking)

Question 27

What is the equation for Attributable risk (AR)?

Answer 27

AR = [ (a)/(a+b) ] - [ (c)/(c+d) ]

Question 28

What is the definition for absolute risk reduction (ARR)?

Answer 28

It’s the difference in risk (not the proportion) attributable to the intervention as compared to a control.

(eg - if 8% of people who receive a placebo vaccine develop flue vs 2% of people who receive a flue vaccine, the ARR = 8% - 2% = 6% or 0.06)

Question 29

What is the ‘number needed to treat’?

Answer 29

Number of patients who need to be treated for 1 patient to benefit. Calculated as 1/ARR

Question 30

What is the ‘number needed to harm’?

Answer 30

It’s the number of patients who need to be exposed to a risk factor for 1 patient to be harmed. Calculated as 1/AR