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Flashcards in Epidemiology Deck (79):
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.

Distribution
Determinants

2

Who is considered the father of epidemiology?

John Snow

3

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

Prevalence

4

___________ refers only to new cases of disease

Incidence

5

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

True

6

How is incidence calculated?

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

7

Risk and attack rate are alternative terms for what?

Incidence

8

How is prevalence calculated?

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

9

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

Subtracting frequencies

10

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

Division (ratio) of frequencies

11

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

Absolute differences

12

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

Risk

13

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

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

So subtract the risk percentages and take absolute value

14

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

ARR/R(unexposed)

15

How would you calculate NNT?

1/ARR

16

How is the risk ratio (RR) calculated?

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

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).

More
Less

18

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

Group comparison orientation
Direction of relationship
Magnitude

19

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

It is always statistically significant!

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%

B. 14%

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%

C. 17.8%

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

A. 0.78

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

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

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

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

25

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

Odds

[A/C or B/D]

26

How is an odds ratio (OR) calculated?

Odds of exposure (in diseased) / Odds of exposure (in non-diseased)

This is the one where you can cross multiply!

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

A. 37/63

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.

Confounder

29

How do you test for confounding?

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

30

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

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

31

How is the crude association calculated?

Simply between exposure and outcome:

(A/A+B) / (C/C+D)

32

How is the adjusted association calculated?

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

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)

Effect modification

34

What is the difference between confounding and effect modification?

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

35

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

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

36

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

Bias

37

What is the most common type of bias?

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]

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?

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

39

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

Null states that there will be no true difference between groups

Alternative states there will be a true difference between groups

40

What are the 2 overall types of study design?

Interventional and observational

41

What is the primary difference between interventional and observational studies?

Interventional = forced group allocation (randomized)

Observational = no forced group allocation

42

Which type of observational study has the most evidence?

Cohort

43

Which observational design has the least evidence?

Case report - followed by cross sectional

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

44

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

Equipoise

45

What are the 4 key principles of bioethics?

Autonomy
Beneficence
Justice
Nonmaleficence

46

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

Case-control

47

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

Controls must be selected irrespective of exposure status!

48

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

Cohort

49

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

Cross-sectional

50

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

Sensitivity

51

How is sensitivity calculated?

Number of true positives / All diseased x 100%

52

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

Specificity

53

How is specificity calculated?

Number of true negatives / All without disease x 100%

54

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

Type 1

55

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

Type 2

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

P

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

Confidence interval

58

What is the correlation test utilized for nominal data?

Contingency coefficient

59

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

Logistic regression

60

What is the survival test utilized for nominal data?

Log-rank

61

What is the regression test utilized for ordinal data?

Multinomial logistic regression

62

What is the regression test utilized for interval data?

Linear regression

63

What is the correlation test utilized for interval data?

Pearson correlation

64

What is the survival test utilized for interval data?

Kaplan-meier

65

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

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

66

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

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

67

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

Post-hoc testing

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

B. Chi-square

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

A. ANOVA

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

D. Student-t

71

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

CONSORT

72

What checklist is utilized by ALL observational studies?

STROBE

73

What are the 3 W's of descriptive epidemiology?

Who
When
Where

74

What are the 2 questions proposed by analytic epidemiology?

Why
How

75

Occurence of disease clearly in excess of normal expectancy

Epidemic

76

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

Outbreak

77

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

Endemic

78

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

Emergency of international concern

79

An epiemic spread worldwide (global health)

Pandemic