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epi > Final > Flashcards

Final Flashcards

1
Q

What is confounding?

A

Confounding is a potential source of bias in epidemiologic studies
serves as an antecedent of both the exposure and the outcome, third variable distorts the true association between the exposure and the disease

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2
Q

What is effect modification?

A

The effect of the exposure on the outcome differs for varying levels according to presence of a third variable; related to biologic differences between two groups

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3
Q

How do you deal with confounding and effect modification?

A

In study design: Confounding - restriction, matching, randomization
In analysis: stratification for both confounding and EMM

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4
Q

Preventative Association

A

Odds Ratio or Risk Ratio is less than 1, meaning the exposure prevents the outcome

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5
Q

Positive Association

A

Odds Ratio or Risk Ratio is greater than 1, meaning the exposure leads to greater risk of delevoping the outcome

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6
Q

What is selection bias?

A

Selection bias occurs when some potential subjects are more likely to be included in the study than others (recruiting patients, can bias OR towards or away from the null)

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7
Q

What is information bias?

A

Information bias occurs when data is collected differently across subjects (recall bias, outcome misclassification)

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8
Q

What are the two types of outcome misclassification?

A

Non-differential: probability of individuals being misclassified is equal across all groups of the study
Differential: probability of being misclassified differs between groups in a study

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9
Q

What are the steps of an outbreak investigation?

A
  1. Prepare for fieldwork
  2. Confirm the existence of an outbreak
  3. Verify diagnosis (define a case)
  4. Find cases, tabulate and orient data: person, place, time
  5. Condust descriptive epidemiology
  6. Formulate and test the hypothesis
  7. Implement and evaulate control measures
  8. Initiate or maintain surveillance
  9. Communicate findings
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10
Q

What are the three parts of the epidemiologic triangle?

A

Host, Agent, Environment

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11
Q

Formula for incidence of EXPOSURE in an ecological study

A

(a+b) / [(a+b)+(c+d)]

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12
Q

Formula for incidence of DISEASE in an ecological study

A

(a+c) / [(a+c)+(c+d)]

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13
Q

What are the advantages of an ecological study?

A

Large-scale trends through time
Hypothesis generating
Can use aggregate, environmental, or global measures
Data is collected by governments and them available for multiple uses
Inexpensive, simple, fast

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14
Q

What are the disadvantages of an ecological study?

A

Cannot make casual interpretations
Impossible to control for potential confounder bias
Ecological fallacy: association that exist at a group level may not exist at an individual level

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15
Q

What is the ecological study design?

A

Examines a group as a unit of analysis to produce correlational measures (trends in population, never individual)

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16
Q

What is the cross-sectional study design?

A

Data is collected at one point in time and includes exposures and outcomes

17
Q

Formula for calculating the prevalence of disease in the exposed persons vs unexposed

A

a / a+b
c / c+d

18
Q

Formula for calculating prevalence of exposure in persons with disease vs without disease

A

a / a+c
b / b+d

19
Q

What are the measures of frequency for a cross-sectional study?

A

Prevalence of outcome: (a+c) / N
Prevalene of exposure: (a+b) / N

20
Q

What is the measure of association for cross-sectional studies?

A

Prevalence odds ratio: ad / bc
POR of outcome: (a/b) / (c/d)
POR of exposure: (a/c) / (b/d)

21
Q

What are the advantages of a cross-sectional study?

A

Permit determination of population characteristics
Useful for diseases that are prevalent and of long duration
Good for generating hypothesis and/or initially testing one

22
Q

What are the disadvantages of the cross-section study design?

A

Not useful for diseases that are rare and or short duration
Temperoal relationship between expsoure and disease in unclear

23
Q

What is the case-control study design?

A

Subjects are selected from a population based on disease status, then it is worked backwards to find who was exposed and unexposed - exposure in determined retrospectively
compares cases to control with respect to exposure

24
Q

What is the unit of observation and analysis of case-control study?

A

Individual

25
Q

What is the measure of frequency for a case-control study design?

A

Prevalence

26
Q

What is the measure of association for a case-control study?

A

Odds Ratio

27
Q

What are the advantages of a case-control study?

A

Used for rare diseases (low prevalence)
Used for diseases with long induction and letent period
Relatively efficient with repect to time and cost
Multiple exposures can be studied at once

28
Q

What are the disadvantages of a case-control study?

A

Disease incidence or risk cannot be obtained directly
Temporal relationship between exposure and disease is unclear
Not useful for rare exposures
Prone to information and selection bias (recall bias)

29
Q

What is the cohort study design?

A

Starts with a group of subjects who lack a positive history of the outcome of interest and are at risk for the outcome; includes at least two observation points (one to determine exposure status and another to determine the number of incident cases)
unit of analysis: individual

30
Q

What is attrition?

A

Type of selection bias in which study participants cemone missing at some point during the follow-up period of a study

31
Q

What are the advantages of a cohort study?

A

Provide a direct estime of risk
Are useful for rare exposures
Can study more than one outcome
Temporal relationships more clear

32
Q

What are the disadvantages of a cohort study?

A

Larger, longer, and more expensive
Prone to certain types of bias (attrition, miscalssification)
Changes in exposure or medical practice can be missed
Not practical for rare outcomes

33
Q

What are the major differences in experimental and observational study design?

A
  1. Manipulation of the study factor (M): meand that the exposure of interest is controlled by the investigator, not the study subjects
  2. Radmonization of study subjects (R): refers to a process in which chance determines the likelihood of subject’s assignment to exposure conditions
34
Q

What are the benefits of randomization?

A

To compare the outcomes in treatment A vs treatment B, other factors should be comparable - the effect on outcome is then only attributable to treatment itself and randomization can achieve it

35
Q

What are the measures of frequency in a randomized control trial?

A

Cumulative incidence: a / a+b
Incidence density: a / person-years

36
Q

What are the measures of association for randomized contorl trials?

A

Risk ratio (based on cumulative incidence)
Rate ratio (based on incidence density)

epi (3 decks)

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