Final Epidemiology

Question 1

Sensitivity

Answer 1

Proportion of persons w/ dz w/ + test

Question 2

Specificity

Answer 2

Proportion of persons w/o dz w/ - test

Question 3

Positive Predictive Value (PPV)

Answer 3

Proportion of pt w/ + test who have the dz

*PPV is closely related to the prevalence

Question 4

Negative Predictive Value (NPV)

Answer 4

Proportion of pt’s w/ - test who do NOT have the dz

Question 5

Sn-N-OUT Rule

Answer 5

Sensitivity is high, you can RULE OUT the dz if test comes back -

Question 6

Sp-P-IN Rule

Answer 6

Specificity high then you can rule in the dz if test comes back +

Question 7

LR+

Answer 7

Probability of + test for person w/ dz divided by probability of + test for person w/o the dz
= Sensitivity / (1 - Specificity)

Question 8

LR-

Answer 8

Probability of - test for person w/ dz divided by probability of - test for person w/o dz
= (1 - Sensitivity) / Specificity

Question 9

LRs to “rule in” dz

Answer 9

> 10: strong
5-10: moderate
2-5: weak

Question 10

LRs to “rule out” dz

Answer 10

0.2 - 0.5: weak
0.1 - 0.2: moderate
< 0.1: strong

Question 11

Parallel Testing

Answer 11

Order several tests @ once, useful for rapid assessment situations

• maximizes sensitivity and NPV
• e.g. - CP in the ED order CK and Troponin, etc.

Question 12

Serial Testing

Answer 12

Order next test on basis of prior result, useful when assessment can be done over time or tests are expensive

• maximizes specificity and PPV
• e.g. - serial troponins for a CP pt in ED under obs

Question 13

Benefits of Screening

Answer 13

Earlier detection leads to better outcome, test has good sensitivity/specificity, burden of dz in community warrants test, resources available to follow-up + tests

Question 14

Primary Prevention

Answer 14

Identify risk factor for dz and reduce exposure, promote resistance
*e.g. - immunization

Question 15

Secondary Prevention

Answer 15

Identify early dz before signs/sx’s start

*e.g. - screen for DM

Question 16

Tertiary Prevention

Answer 16

Dz has been identified but prevent advanced development, side effects, and outcomes etc.
*e.g. - pt w/ DM educate to prevent loss of sight/limb

Question 17

Cumulative Incidence (Risk)

Answer 17

Probability of an individual developing dz during a specific timeframe, using # of persons @ risk for the denominator

Question 18

Incidence Density (person-time)

Answer 18

Probability of an individual developing a dz during specific period of time using total person time as the denominator

Question 19

Case Reports

Answer 19

Describe the experience of a single pt (n = 1) w/ an interesting finding
*no comparison

Question 20

Case Series

Answer 20

Describe the experience of a group of pt’s (n > 1) w/ similar dx’s
*no comparison group

Question 21

Cross-Sectional Studies

Answer 21

Aka Prevalence Study, exposure and dz status assesed @ single point in time, individual is unit of observation and analysis, no cause-effect and no incidence known

• dz or no dz -or- exposed or unexposed
• common analysis is Chi square

Question 22

Case-Control Study

Answer 22

Key comparison: Dz vs. No Dz
- no prevalence or incidence assessed; measure risk of exposure to risk factors in dz group vs the no dz group retrospectively

Question 23

Cohort Study

Answer 23

Key comparison: Risk factor vs. No Risk Factor, groups followed over time to see who ends up developing the dz, assesses incidence and causality but not prevalence

Question 24

Intention-to-treat Analysis

Answer 24

Analyze according to group initially assigned regardless of whether they received tx

Question 25

Explanatory Analysis

Answer 25

Analyze according to tx actually received, regardless of randomization

Question 26

Efficacy setting

Answer 26

Analyzing tx in ideal setting

Question 27

Effectiveness setting

Answer 27

Analyze tx in ordinary circumstances; usual pt care

Question 28

Relative Risk Reduction

Answer 28

Describes the magnitude of the effect; represents the % reduction in risk of studied outcome achieved by the use of the intervention

Question 29

Absolute Risk Reduction

Answer 29

Describes the risk difference in outcome btwn pt’s who have undergone 1 therapy and those who have not

Question 30

Number Needed to Treat

Answer 30

NNT = 1/AR

*if you’re looking @ the treatment

Question 31

Number Needed to Harm

Answer 31

NNH = 1/AR

*if you’re looking @ exposure

Question 32

Randomized Clinical Trial

Answer 32

Randomly allocated into “intervention” or “control” group to receive tx or not
- control can be placebo group or standard of care group to compare the tx group to

Question 33

Measures used to describe Prognosis

Answer 33

• 5 yr survival
• median survival
• response to tx (improvement)
• time to recurrence
• case fatality
• dz-specific mortality

Question 34

Prognosis

Answer 34

Set of probabilities that predict a worse outcome once a dz is present

Question 35

Survival Curve

Answer 35

AUC is # of person-years lived by population studies (probability of events is dependent on the length of follow-up)
e.g. - time to recurrence, time to remission, time to illness

Question 36

Censored

Answer 36

When pt is lost from a study @ any point in time and are no longer counted in the denominator from that point forward; they are removed from denominator before the probability of survival is calculated for a given period

Question 37

Equipoise

Answer 37

Randomization is ethical when there is no compelling reason to believe that either of the randomly allocated tx’s is better than the other

Question 38

Observational studies show association and:

Answer 38

• exposure precedes dev of dz
• strength of assoc
• dose-response relationship is apparent
• consistency of findings from study to study
• biological plausibility
• findings are c/w other studies and/or types of data

Question 39

Odds Ratio

Answer 39

OR = 1: no association btwn risk and outcome
OR > 1: increased risk of exposure in cases compared to control
OR < 1: decreased risk of exposure in cases compared to control