Epidemiology Flashcards
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
Who is considered the father of epidemiology?
John Snow
_____________ refers to existing cases of disease + New cases of disease
Prevalence
___________ refers only to new cases of disease
Incidence
T/F: Both incidence and prevalence are proportions and factor in the “at risk” or “base” population in the denominator
True
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
Risk and attack rate are alternative terms for what?
Incidence
How is prevalence calculated?
Number of existing cases of a disease / Number of persons in population
In terms of measures of association, how is an absolute difference calculated?
Subtracting frequencies
In terms of measures of association, how are relative differences calculated?
Division (ratio) of frequencies
Of absolute differences and relative differences, which will always be smaller?
Absolute differences
____________ is the probability of an outcome in an individual group (i.e. Exposed or non-exposed)
Risk
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
In terms of measures of association, how is relative risk reduction (RRR) determined?
ARR/R(unexposed)
How would you calculate NNT?
1/ARR
How is the risk ratio (RR) calculated?
Risk of outcome (in exposed) / Risk of outcome (in non-exposed)
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
What are the 3 important components of interpreting ratios (RR/OR/HR)?
Group comparison orientation
Direction of relationship
Magnitude
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!
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%
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%
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
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
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
________ 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]
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!
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
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
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
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
How is the crude association calculated?
Simply between exposure and outcome:
A/A+B) / (C/C+D
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
___________ ____________ 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
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
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
___________ is a systematic (non-radnom) error in study design or conduct leading to erroneous results; and distorts the relationship between exposure and outcome
Bias
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]
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)
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
What are the 2 overall types of study design?
Interventional and observational
What is the primary difference between interventional and observational studies?
Interventional = forced group allocation (randomized)
Observational = no forced group allocation
Which type of observational study has the most evidence?
Cohort
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
__________ refers to genuine confidence that an intervention may be worthwhile (risk vs. benefit) in order to use it in humans
Equipoise
What are the 4 key principles of bioethics?
Autonomy
Beneficence
Justice
Nonmaleficence
What type of observational study design assigns groups based on disease status?
Case-control
What is the most important thing to consider when selecting controls for a case-control study?
Controls must be selected irrespective of exposure status!
What type of observational study design performs group allocation based on exposure status or group membership?
Cohort
What type of observational study design is also known as a PREVALENCE study?
Cross-sectional
_______________ is a measure of how well a test can detect the presence of disease when in fact disease is present
Sensitivity
How is sensitivity calculated?
Number of true positives / All diseased x 100%
___________ refers to how well a test can detect absence of disease when in fact the disease is absent
Specificity
How is specificity calculated?
Number of true negatives / All without disease x 100%
A _________ error is made when rejecting the null hypothesis when it is actually true and you should have accepted it
Type 1
A ______ error is not rejecting the null hypothesis when it is actually false and you should have rejected it!
Type 2
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
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
What is the correlation test utilized for nominal data?
Contingency coefficient
What is the prediction/association (regression) test for nominal data?
Logistic regression
What is the survival test utilized for nominal data?
Log-rank
What is the regression test utilized for ordinal data?
Multinomial logistic regression
What is the regression test utilized for interval data?
Linear regression
What is the correlation test utilized for interval data?
Pearson correlation
What is the survival test utilized for interval data?
Kaplan-meier
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
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
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
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
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
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
What checklist is utilized by most (if not all) interventional studies?
CONSORT
What checklist is utilized by ALL observational studies?
STROBE
What are the 3 W’s of descriptive epidemiology?
Who
When
Where
What are the 2 questions proposed by analytic epidemiology?
Why
How
Occurence of disease clearly in excess of normal expectancy
Epidemic
An epidemic limited to a localized increase in the occurence of disease (sometimes called a cluster)
Outbreak
Constant presence of disease within a given area or population in excess of normal levels in other areas
Endemic
An epidemic that alerts the world to the need for high vigilance (pre-pandemic label)
Emergency of international concern
An epiemic spread worldwide (global health)
Pandemic
