Biostats

Question 1

A variable or attribute that increases the probability of developing a disease or injury

Answer 1

Risk factor

Question 2

The likelihood of an event occurring under specific conditions (%)

Answer 2

Absolute risk

Question 3

Formula for absolute risk

Answer 3

(a+c)/(a+b+c+d)

Question 4

Used to measure the probability of an individual developing an outcome in a study population

Answer 4

Absolute risk

Question 5

Absolute risk is used in what kind of studies?

Answer 5

Cohort studies

Question 6

Measures used to quantify the strength of a relationship between two variables

Answer 6

Measures of association (RR, OR, HR)

Question 7

What are the estimates of association strength?

Answer 7

• relative risk
• odds ratio
• hazard ratio

Question 8

RR, OR, and HR are considered statistically significant if the p-value is

Answer 8

p value is < 0.05

Question 9

Formula for relative risk

Answer 9

(a/(a+b)) / (c/(c+d))

Question 10

Compares the risk of an outcome in those with the exposure to those without the exposure

Answer 10

Relative risk

Question 11

Used to measure how strongly a risk factor is associated with an outcome (death, injury, disease) OR to help establish disease etiology

Answer 11

relative risk

Question 12

The ratio of the probability of an outcome occurring in an exposed group to the probability of the outcome occurring in an unexposed group (exposed/unexposed)

Answer 12

Relative risk (risk ratio)

Question 13

What type of study uses relative risk?

Answer 13

• Cohort studies
• RCT

Question 14

What kind of studies can NOT be used to calculate relative risk?

Answer 14

Case-control studies - they do not track participants over time so they cannot be used to calculate relative risk

Question 15

R > 1 means

Answer 15

incidence of disease is higher in the exposed group so exposure INCREASES risk of outcome

Question 16

R < 1 means

Answer 16

incidence of disease is lower in the exposed group so exposure DECREASES the risk of outcome

Question 17

Odds of exposure in individuals with disease divided by the odds of exposure in individuals without disease

Answer 17

Odds ratio (OR)

Question 18

The probability of an event occurring divided by the probability of an event NOT occurring

Answer 18

odds

Question 19

Used to measure the strength of an association between a risk factor an an outcome (odds of having the exposure in those with the outcome vs those without the outcome)

Answer 19

Odds ratio

Question 20

What kind of studies use odds ratio?

Answer 20

Case-control studies

Question 21

Formula for odds of exposure in individuals with disease (case group)

Answer 21

exposure in individuals with disease divided by no exposure in individuals with disease = a/c

Question 22

Formula for odds of exposure in individuals without disease (control group)

Answer 22

exposure in individuals without disease divided by no exposure in individuals without disease = b/d

Question 23

Formula for odds ratio

Answer 23

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

Question 24

OR = 1 means

Answer 24

The outcome is equally likely in exposed and unexposed individuals

Question 25

OR > 1 means

Answer 25

The outcome is more likely to occur in exposed individuals

Question 26

OR < 1 means

Answer 26

The outcome is less likely to occur in exposed individuals

Question 27

What is the rare disease assumption?

Answer 27

The assumption that if the outcome (disease prevalence) is rare, the incidence of that outcome is low and the OR is approximately the same as the RR.

Question 28

A measure of the effect of an intervention on an outcome at any given point in time during the study period

Answer 28

Hazard ratio

Question 29

Used to help determine how long it takes for an event to occur in individuals in the case group, compared to the control group

Answer 29

Hazard ratio

Question 30

HR = 1 means

Answer 30

no relationship

Question 31

HR > 1 means

Answer 31

The outcome of interest is more likely to occur in exposed individuals

Question 32

HR < 1 means

Answer 32

The outcome of interest is less likely to occur in exposed individuals

Question 33

What are the estimates of population impact?

Answer 33

- attributable risk - relative risk reduction - absolute risk reduction - number needed to treat - number needed to harm

Question 34

The absolute risk attributable to exposure in the exposed group calculated as incidence rate in the exposed group - incidence rate in the unexposed group

Answer 34

Attributable risk

Question 35

Used to measure the excess risk of an outcome that can be attributed to the exposure (how much of the disease can be attributed to the exposure)

Answer 35

attributable risk (AR)

Question 36

Formula for attributable risk (AR)

Answer 36

a/(a+b) - c/(c+d)

Question 37

The difference in risk attributable to an exposure as compared to non-exposure (risk in non-exposed group - risk in exposed group)

Answer 37

Absolute risk reduction (ARR)

Question 38

Used to show the risk without treatment as well as the risk associated with treatment

Answer 38

absolute risk reduction (risk difference)

Question 39

What kind of studies use absolute risk reduction?

Answer 39

- cohort studies - cross sectional studies - clinical trials

Question 40

Formula for absolute risk reduction (ARR)

Answer 40

c/(c+d) - a/(a+b)

Question 41

Measure of risk that refers to proportion of decreased risk due to an intervention compared to the control group

Answer 41

Relative risk reduction (RRR)

Question 42

Used to determine how much the treatment reduces the risk of negative outcomes

Answer 42

relative risk reduction (RRR)

Question 43

Formula for relative risk reduction (RRR)

Answer 43

1-RR

Question 44

Relative risk reduction is used in what kind of studies?

Answer 44

- cohort studies - cross-sectional studies

Question 45

Measure of risk that refers to the number of individuals that must be treated in a particular time period for one person to benefit from treatment

Answer 45

Number needed to treat (NNT)

Question 46

Used to compare the effectiveness of different treatments

Answer 46

number needed to treat

Question 47

Formula for NNT

Answer 47

1/ARR

Question 48

What kind of studies use NNT?

Answer 48

clinical trials

Question 49

Measure of risk that refers to the number of individuals who need to be exposed to a certain risk factor before one person develops disease or injury

Answer 49

Number needed to harm (NNH)

Question 50

Formula for NNH

Answer 50

1/AR

Question 51

Used to determine the potential harms of an intervention

Answer 51

NNH

Question 52

What kind of studies use NNH?

Answer 52

clinical trials

Question 53

The proportion of individuals WITH the disease who actually test positive (true positive rate)

Answer 53

sensitivity

Question 54

The proportion of individuals WITHOUT the disease who actually test negative (true negative rate)

Answer 54

Specificity

Question 55

A test with a high ____ can be used to confirm the diagnosis.

Answer 55

specificity

Question 56

A test with a high ____ can be used to screen for a disease.

Answer 56

sensitivity

Question 57

Formula for Sensitivity

Answer 57

TP/(TP+FN)

Question 58

Formula for Specificity

Answer 58

TN/(FP+TN)

Question 59

Formula for positive predictive value (PPV)

Answer 59

TP/(TP+FP)

Question 60

Formula for negative predictive value (NPV)

Answer 60

TN/(TN+FN)

Question 61

The probability that a patient has a specific disease before the result of the test is known.

Answer 61

Pretest probability

Question 62

A higher pretest probability ___ the NPV and ___ the PPV.

Answer 62

decreases; increases

Question 63

A lower pretest probability ____ the NPV and ___ the PPV.

Answer 63

increases; decreases