Epidemiology

Question 1

Epidemiology is a public health-discipline basic science which studies the ______________ and ___________ of disease in populations to control disease and illness and promote health.

Answer 1

Distribution

Determinants

Question 2

Who is considered the father of epidemiology?

Answer 2

John Snow

Question 3

_____________ refers to existing cases of disease + New cases of disease

Answer 3

Prevalence

Question 4

___________ refers only to new cases of disease

Answer 4

Incidence

Question 5

T/F: Both incidence and prevalence are proportions and factor in the “at risk” or “base” population in the denominator

Answer 5

True

Question 6

How is incidence calculated?

Answer 6

Number of new cases of illness / Number of people at risk of illness (or in pop)

***Remember to subtract out from starting population those who already have disease or are immune to the disease

Question 7

Risk and attack rate are alternative terms for what?

Answer 7

Incidence

Question 8

How is prevalence calculated?

Answer 8

Number of existing cases of a disease / Number of persons in population

Question 9

In terms of measures of association, how is an absolute difference calculated?

Answer 9

Subtracting frequencies

Question 10

In terms of measures of association, how are relative differences calculated?

Answer 10

Division (ratio) of frequencies

Question 11

Of absolute differences and relative differences, which will always be smaller?

Answer 11

Absolute differences

Question 12

____________ is the probability of an outcome in an individual group (i.e. Exposed or non-exposed)

Answer 12

Risk

Question 13

In terms of measures of association, how is an absolute risk reduction (ARR) determined?

Answer 13

ARR is the risk difference of the outcome attributable to exposure difference between groups

So subtract the risk percentages and take absolute value

Question 14

In terms of measures of association, how is relative risk reduction (RRR) determined?

Answer 14

ARR/R(unexposed)

Question 15

How would you calculate NNT?

Answer 15

1/ARR

Question 16

How is the risk ratio (RR) calculated?

Answer 16

Risk of outcome (in exposed) / Risk of outcome (in non-exposed)

Question 17

All ratios have the property that if ratio is 1.0, then the event/outcome is equally likely for both groups. If the ratio is >1.0, then the event/outcome is ________ likely to occur in the comparison group (numerator). If the ratio is >1.0, then the event/outcome is ________ likely to occur in the comparison group (numerator).

Answer 17

More

Less

Question 18

What are the 3 important components of interpreting ratios (RR/OR/HR)?

Answer 18

Group comparison orientation
Direction of relationship
Magnitude

Question 19

What does it mean if both values of an RR/OR/HR are on the same side of 1.0?

Answer 19

It is always statistically significant!

Question 20

Of 4,645 patients randomized to take Ramipril and 4,652 randomized to take a placebo, 651 in the Ramipril group and 826 in the placebo group had the combined endpoint of MI. What is the risk of the combinded outcome in the Ramipril group (exposed)?

A. 9.5%
B. 14.0%
C. 17.8%
D. 25.6%
E. 33.2%

Answer 20

B. 14%

Question 21

Of 4,645 patients randomized to take Ramipril and 4,652 randomized to take a placebo, 651 in the Ramipril group and 826 in the placebo group had the combined endpoint of MI. What is the risk of the combined outcome in the placebo group (unexposed)?

A. 9.5%
B. 14.0%
C. 17.8%
D. 25.6%
E. 33.2%

Answer 21

C. 17.8%

Question 22

Of 4,645 patients randomized to take Ramipril and 4,652 randomized to take a placebo, 651 in the Ramipril group and 826 in the placebo group had the combined endpoint of MI. What is the relative risk of the combined outcome between the 2 groups?

A. 0.78
B. 0.95
C. 1.27
D. 1.96
E. 2.23

Answer 22

A. 0.78

Question 23

Of 4,645 patients randomized to take Ramipril and 4,652 randomized to take a placebo, 651 in the Ramipril group and 826 in the placebo group had the combined endpoint of MI. (RR, 0.78; 95% CI 0.70-0.86; p<0.001). Which is an appropriate interpretation of the ratio of risks between the two groups?

A. The placebo group had a 22% reduced risk of the combined outcome
B. The ramipril group had a 42% greater risk of the combined outcome
C. The placebo group had a 37% greater risk of the combined outcome
D. The ramipril group had a 22% reduced risk of the combined outcome
E. The placebo group had a 1.27x lower risk of the combined outcome

Answer 23

D. The ramipril group had a 22% reduced risk of the combined outcome

Question 24

A hypthetical retrospective cohort study was conducted in 100 subjects living in a small Ethiopian village. The study evaluated the frequency of developing intestinal infectious disease associated with exposure to contaminated pond water. The study determined the risk ratio (RR) to be 2.54. Which of the following is the most appropriate interpretation of this finding?

A. Compared to subjects not exposed to the pond water, subjects exposed to the contaminated pond water were 2.54x more likely to develop intestinal disease
B. Compared to subjects not exposed to the pond water, subjects exposed to contaminated water were 54% more likely to develop intestinal disease
C. Compared to subjects exposed to contaminated pond water, subjects not exposed to pond water were 62.5% less likely to develop intestinal disease
D. Compared to subjects exposed to contaminated pond water, subjucts not exposed were 2.54x more likely to develop intestinal disease
E. Compared to subjects not exposed to pond water, subjects exposed to contaminated pond water were 200% more likely to develop intestinal disease

Answer 24

A. Compared to subjects not exposed to the pond water, subjects exposed to the contaminated pond water were 2.54x more likely to develop intestinal disease

Question 25

________ is a measure of association indicating the frequency of an outcome occurring vs. NOT occurring. This value is a ratio

Answer 25

Odds [A/C or B/D]

Question 26

How is an odds ratio (OR) calculated?

Answer 26

Odds of exposure (in diseased) / Odds of exposure (in non-diseased) This is the one where you can cross multiply!

Question 27

Researchers randomly selected 100 pts with newly diagnosed oropharyngeal cancer and 200 pts without cancer. Of the cancer pts, 63 were negative and 37 were positive for any oral HPV infection. Of the controls, 189 were negative and 11 were positive for any oral HPV infection. What is the odds of HPV infection in those with oropharyngeal cancer? ``` A. 37/63 B. 63/189 C. 189/11 D. 36/37 E. 37/100 ```

Answer 27

A. 37/63

Question 28

A _____________ is a 3rd variable that distorts an association (RR/OR/HR) between the exposure and the outcome; aka it makes the groups not exchangeable in terms of their associations.

Answer 28

Confounder

Question 29

How do you test for confounding?

Answer 29

Compare the crude vs. adjusted measures of association between exposure and outcome. These values will be different by 15% if confounding IS present

Question 30

If your crude value is calculated to be 2.0 and your adjusted value is calculated to be 1.5, is confounding present?

Answer 30

YES, 2.0-1.5/2.0 = 25%, since this is greater than 15% there IS confounding present

Question 31

How is the crude association calculated?

Answer 31

Simply between exposure and outcome: | A/A+B) / (C/C+D

Question 32

How is the adjusted association calculated?

Answer 32

This is the OR/RR between exposure and outcome for ALL strata. Same calculation as crude, but each individual strata is compared to the overall crude value

Question 33

___________ ____________ is a 3rd variable that, when present, modifies the magnitude of effect of a true association by varying it within different levels of a 3rd variable (modifies the effect across the strata)

Answer 33

Effect modification

Question 34

What is the difference between confounding and effect modification?

Answer 34

With confounding, the researcher is able to control for it. With EM, the 3rd variable should be described and reported at each level rather than controlled for

Question 35

How are you able to tell if effect modification is present?

Answer 35

Compare each of the strata-specific measures of associations (OR/RR) between each other [while referencing adjusted measure of association] The measure of association (RR/OR) between the LOWEST and HIGHEST strata of the effect-modifying variable will be 15% different if effect modification IS present

Question 36

___________ is a systematic (non-radnom) error in study design or conduct leading to erroneous results; and distorts the relationship between exposure and outcome

Answer 36

Bias

Question 37

What is the most common type of bias?

Answer 37

Selection bias - the way that study subjects are selected generates differences in groups [key examples: healthy-worker bias, self-selection/participant bias, control selection bias]

Question 38

There are 5 criteria known as Hill's criteria (guidelines) utilized in the causal inference process. The higher the number of criteria met, the more likely an association is to be causal. What are these 5 criteria?

Answer 38

``` Strength (size of association) Consistency (reproducibility) Temporality (does cause precede outcome) Biologic gradient (dose-response) Plausibility (biologic feasibility) ```

Question 39

What is the difference between a null hypothesis and an alternative hypothesis?

Answer 39

Null states that there will be no true difference between groups Alternative states there will be a true difference between groups

Question 40

What are the 2 overall types of study design?

Answer 40

Interventional and observational

Question 41

What is the primary difference between interventional and observational studies?

Answer 41

Interventional = forced group allocation (randomized) Observational = no forced group allocation

Question 42

Which type of observational study has the most evidence?

Answer 42

Cohort

Question 43

Which observational design has the least evidence?

Answer 43

Case report - followed by cross sectional so from least to most: case report, cross sectional, ecological, case-control, cohort

Question 44

__________ refers to genuine confidence that an intervention may be worthwhile (risk vs. benefit) in order to use it in humans

Answer 44

Equipoise

Question 45

What are the 4 key principles of bioethics?

Answer 45

Autonomy Beneficence Justice Nonmaleficence

Question 46

What type of observational study design assigns groups based on disease status?

Answer 46

Case-control

Question 47

What is the most important thing to consider when selecting controls for a case-control study?

Answer 47

Controls must be selected irrespective of exposure status!

Question 48

What type of observational study design performs group allocation based on exposure status or group membership?

Answer 48

Cohort

Question 49

What type of observational study design is also known as a PREVALENCE study?

Answer 49

Cross-sectional

Question 50

_______________ is a measure of how well a test can detect the presence of disease when in fact disease is present

Answer 50

Sensitivity

Question 51

How is sensitivity calculated?

Answer 51

Number of true positives / All diseased x 100%

Question 52

___________ refers to how well a test can detect absence of disease when in fact the disease is absent

Answer 52

Specificity

Question 53

How is specificity calculated?

Answer 53

Number of true negatives / All without disease x 100%

Question 54

A _________ error is made when rejecting the null hypothesis when it is actually true and you should have accepted it

Answer 54

Type 1

Question 55

A ______ error is not rejecting the null hypothesis when it is actually false and you should have rejected it!

Answer 55

Type 2

Question 56

If the ____ value is less than the pre-selected alpha value (customarily 0.05 or 5%), then we can say that it is statistically significant

Answer 56

P

Question 57

The ___________ ___________ is a value selected a priori that states at which percentage you feel the true difference or relationship between groups is contained within a certain range

Answer 57

Confidence interval

Question 58

What is the correlation test utilized for nominal data?

Answer 58

Contingency coefficient

Question 59

What is the prediction/association (regression) test for nominal data?

Answer 59

Logistic regression

Question 60

What is the survival test utilized for nominal data?

Answer 60

Log-rank

Question 61

What is the regression test utilized for ordinal data?

Answer 61

Multinomial logistic regression

Question 62

What is the regression test utilized for interval data?

Answer 62

Linear regression

Question 63

What is the correlation test utilized for interval data?

Answer 63

Pearson correlation

Question 64

What is the survival test utilized for interval data?

Answer 64

Kaplan-meier

Question 65

With nominal data, what tests can be done for 2 groups or 3+ groups of independent data?

Answer 65

2 groups: pearson's chi square | 3+ groups: chi square

Question 66

What types of tests are used for interval data with 2 groups vs. 3+ groups of independent data?

Answer 66

2 groups: student t | 3+ groups: ANOVA/MANOVA

Question 67

What type of testing is done after a statistically significant finding in 3 or more comparisons to determine which group is different?

Answer 67

Post-hoc testing

Question 68

Which of the following tests would be most appropriate if researchers wished to compare the proportion of patients in each of the 2 treatment groups who developed (or didn't) a recurrent VTE? ``` A. ANOVA B. Chi-square C. Kruskal Wallis D. Multinomial logistic regression E. Freidman test ```

Answer 68

B. Chi-square

Question 69

Which of the following tests would be most appropriate if the researchers wished to compare, between the 2 treatment groups, the number of days the patient was on therapy before they had a VTE recurrence? ``` A. ANOVA B. Chi-square C. Kruskal-Wallis D. Multinomial regression E. Freidman ```

Answer 69

A. ANOVA

Question 70

Which of the following tests would be most appropriate if researchers wished to compare the mean blood sugar between treatment groups (assume normal distribution and equal variances)? ``` A. Cochran B. Fisher's exact C. Kruskal wallis D. Student-t E. Mann-whitney ```

Answer 70

D. Student-t

Question 71

What checklist is utilized by most (if not all) interventional studies?

Answer 71

CONSORT

Question 72

What checklist is utilized by ALL observational studies?

Answer 72

STROBE

Question 73

What are the 3 W's of descriptive epidemiology?

Answer 73

Who When Where

Question 74

What are the 2 questions proposed by analytic epidemiology?

Answer 74

Why | How

Question 75

Occurence of disease clearly in excess of normal expectancy

Answer 75

Epidemic

Question 76

An epidemic limited to a localized increase in the occurence of disease (sometimes called a cluster)

Answer 76

Outbreak

Question 77

Constant presence of disease within a given area or population in excess of normal levels in other areas

Answer 77

Endemic

Question 78

An epidemic that alerts the world to the need for high vigilance (pre-pandemic label)

Answer 78

Emergency of international concern

Question 79

An epiemic spread worldwide (global health)

Answer 79

Pandemic