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Boards > Biostats > Flashcards

Biostats Flashcards

1
Q

Study that is determining the frequency of disease at a particular point in time (prevalence), purely observational

A

cross-sectional study

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2
Q

Study that compares a group of people with disease to a group without disease, looks for prior exposures or risk factors, retrospective and observational

A

Case-control study

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3
Q

Study that compares a group with a given exposure exposure or risk factor to a group without that exposure, determines whether exposure affects likelihood of disease

A

Cohort study

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4
Q

What study type determines the odds ratio?

A

case-control (group of people with dz vs. without dz)

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5
Q

What study type determines the relative risk?

A

cohort study (group with exposure to risk factor vs. group without exposure)

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6
Q

What type of study always involves an intervention?

A

clinical trial

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7
Q

Phase I drug trial

A

Is this drug safe?

-test drug on healthy volunteers

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8
Q

Phase II drug trial

A

Is this drug effective?

-test drug in group of pts with disease

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9
Q

Phase III drug trial

A

Is this drug as good or better than what already exists?

-large number of pts randomly assigned to treatment or placebo group

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10
Q

Phase IV drug trial

A

Can the drug stay on the market?

-postmarketing surveillance of rare or long-term side effects

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11
Q

Sensitivity

A

proportion of people with disease who test positive

TP / TP + FN

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12
Q

Best type of screening test has high (sensitivity or specificity)

A

sensitivity

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13
Q

Best type of diagnostic test has high (sensitivity or specificity)

A

specificity

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14
Q

Specificity

A

proportion of people without dz who test negative

TN / TN + FP

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15
Q

What is PPV?

A

proportion of positive test results that are true positives

PPV = TP / TP + FP

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16
Q

What is NPV?

A

proportion of negative test results that are true negatives

NPV = TN / TN + FN

17
Q

How does an increase in disease prevalence affects PPV and NPV?

A

increase in PPV, decrease in NPV

18
Q

What is incidence?

A 
# of new cases / # of people at risk 
-incidence looks at new cases in a given period of time
19
Q

What is prevalence?

A 
# of existing cases / total # of people in a population
-looks at all current cases
20
Q

What happens to incidence and prevalence for a disease with short duration (i.e. flu)?

A

prevalence ~ incidence

21
Q

What happens to incidence and prevalence for a disease with long duration (i.e. COPD)?

A

prevalence > incidence

22
Q

Equation for Confidence intervals

A

CI = Mean +/- Z-score x SEM

Z = 2 for 95% confidence intervals

23
Q

Equation for SEM

A

SEM = SD / square root of N

24
Q

What is Type I error (alpha)?

A

false-positive error - stating there is a difference in an effect when none exists

25
Q

What is a Type II error (beta)?

A

false-negative error - stating there is no difference when one exists

26
Q

What is power?

A

probability of rejecting the null hypothesis when it is false

27
Q

What increases power?

A

increase sample size, increase in expected effect size, increase in precision of measurement

calculate by taking 1 - beta error

28
Q

Equation for odds ratio

A

a/c / b/d

odds that group with dz was exposed to risk factor divided by odds that group without dz was exposed to risk factor

29
Q

Relative risk

A

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

risk of developing a dz if you are exposed to a risk factor divided by risk in unexposed group

30
Q

Attributable risk

A

a/a+b - c/c+d

difference in risk between exposed and unexposed (how much of dz occurrences are attributable to exposure)

31
Q

Relative risk reduction

A

RR - 1

proportion of risk reduction attributable to intervention as compared to control

32
Q

Absolute risk reduction

A

c/c+d - a/a+b

difference in risk attributable to the intervention as compared to a control

33
Q

Number needed to treat

A

NNT = 1/ARR

34
Q

Number needed to harm

A

NNH = 1/AR

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