Biostats

Question 1

Cross-Sectional Study

Answer 1

Frequency of disease and frequency of risk-related factors are assessed in the present.

Measures DISEASE PREVALENCE.

Question 2

Case-Control Study

Answer 2

Compares a group of people with disease to a group without disease.

Measures ODDS RATIO

*Controls and cases are selected based on DISEASE STATUS.

Question 3

Cohort Study

Answer 3

Compares a group with a given EXPOSURE or RISK FACTOR to a group without such exposure.

Measures RELATIVE RISK

Question 4

Crossover Study

Answer 4

Compares the effect of a serioes of 2 or more treatments on a participant. Washout period occurs between each treatment.

Allows participants to serve as their own controls.

Question 5

Twin Concordance Study

Answer 5

Compares the frequency with which both monozygotic twins vs. both dizygotic twins develop the same disease.

Measures HERITABILITY and INFLUENCE OF ENVIRONMENTAL FACTORS

Question 6

Adoption Study

Answer 6

Compares siblings raised by biological vs. adoptive parents.

Measures HERITABILITY and INFLUENCE OF ENVIRONMENTAL FACTORS.

Question 7

Clinical Trial - Phase 1

Answer 7

Assesses safety, toxicity, pharmacokinetics, and pharmacodynamics.

Question 8

Clinical Trial - Phase 2

Answer 8

Assesses treatment efficacy, optimal dosing and adverse effects.

Question 9

Clinical Trial - Phase 3

Answer 9

Compares the new treatment to the current standard of care

Question 10

Clinical Trial - Phase 4

Answer 10

Detects rare or long-term adverse effects

Question 11

Sensitivity

Answer 11

TRUE POSITIVE RATE - portion of all peope with the disease who test positive, or the probability that when the disease is present, the test is positive.

SN-N-OUT: highly sensitive test, when negative, rules OUT disease.

TP/ (TP + FN)

Good for screening tests!

Question 12

Specificity

Answer 12

TRUE NEGATIVE RATE- Proportion of all people without disease who test negative, or the probability that when the disease is absent, the test is negative

SP-P-IN: high specific test, when positive, rules IN disease.

TN/ (TN + FP)

Question 13

Positive Predictive Value

Answer 13

Probability that a person who has a positive test result actually has the disease.

PPV= TP / (TP+FP)

Question 14

Negative Predictive Value

Answer 14

Probability that a person with a negative test result actually does not have the disease.

NPV= TN/(TN+FN)

Question 15

Lowering Cutoff Value

Answer 15

Increases FP, Decreases FN

Increases sensitivity and NPV

Decreases specificity and PPV

Question 16

Raising Cutoff Value

Answer 16

Increasing FN, Decreasing FP

Increases specificity and PPV

Decreases sensitivity and NPV

Question 17

Likelihood Ratios

Answer 17

Likelihood that a given test result would be expected in a patient with the target disorder compared to the liklihood that the same result would be expected in a patient without the target disorder.

LR+= sensitivity/ (1-specificity)= TP rate/FP rate

LR-= (1-sensitivity) / specificity = FN rate/ TN rate

If LR+ >10 and/or LR- <0.1 indicate a very useful diagnostic test

Question 18

Odds Ratio

Answer 18

Depicts odds of certain outcome given an exposure vs the odds of the outcome in the absence of that exposure

Associate with CASE-CONTROL STUDIES

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

Question 19

Relative Risk

Answer 19

Risk of developing disease in the exposed group divided by the risk in the unexposed group.

Associate with COHORT STUDIES (follows people over time)

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

RR= 1 : no association b/w exposure and disease

RR>1 : exposure associated with increased disease occurrence

RR<1 : exposure associated with decreased disease occurrence

Question 20

Relative Risk Reduction

Answer 20

The proportion of risk reduction attributable to the intervention as compared to a control

RRR= 1- RR

Question 21

Attributable Risk

Answer 21

The difference between exposed and unexposed groups

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

AR%

Question 22

Absolute Risk Reduction

Answer 22

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

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

Question 23

Number Needed to Treat

Answer 23

Number of patients who need to be treated for 1 patient to benefit

NNT= 1/ARR

Question 24

Number Needed to Harm

Answer 24

Numer of patients who need to be exposed to a risk factor for 1 patient to be harmed

NNH= 1/AR

Question 25

Case Fatality Rate

Answer 25

Percentage of deaths that occur over the disease course

CFR% = deaths/cases x100

Question 26

Incidence

Answer 26

Looks at NEW CASES

Incidence= (#new cases) / (# of people at risk)

Question 27

Prevalence

Answer 27

Looks at ALL CURRENT CASES in a given population

Prevalence= (# existing cases) / (Total # people in population)

Question 28

Maternal Mortality Rate

Answer 28

MMR= (# maternal deaths) / (# live births)