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CHEP 350 > Post-midterm 2 > Flashcards

Post-midterm 2 Flashcards

1
Q

When to use odds ratio and rate ratio to calculate attributable risk %?

A

When frequency of the outcome is low (<0.10) the odds ratio may be used to estimate the risk ratio

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2
Q

What is ecologic fallacy

A

An ecologic fallacy occurs when one concludes incorrectly that an association found at the group or aggregate level also applies at the individual level.

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3
Q

When are ecological studies undertaken

A
  1. Only aggregate information on exposure is available
  2. The exposure of interest varies only at the population level
  3. Interested in both individual and group exposures (multi-level studies)
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4
Q

Limitations of ecological studies

A

Ecologic fallacy
Sources of exposure or outcome may not be accurate
Difficult to control for confounders, especially at individual level
May be impossible to establish temporal sequence

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5
Q

Strengths of ecological study

A

Quick and low cost
Generate hypotheses for further study at the individual level
Some associations may only be examined at the aggregate level

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6
Q

What is a cause

A

An event condition or characteristic that preceded the disease event and without which the disease event would not have occurred at all until some later time

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7
Q

What are extraneous variables

A

Variables that occur outside of the exposure-disease relationship
Examples: Confounding variables, effect modifying variables, neither

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8
Q

What is confounding

A

Confounding is an intermixing of the effect of an exposure with that of an independent risk factor for the outcome (disease), leading to an estimated association that no longer reflects the causal impact of the exposure of interest

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9
Q

What is mediation

A

Represents an intermediate step in the causal sequence between the exposure and outcome. Mediating variables are links in a chain of causal events connecting exposure to disease

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10
Q

Ways to control confounding in the design phase

A

◼ Restriction
◼ Randomization
◼ Matching

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11
Q

Ways to control confounding in the analysis phase

A

◼ Standardization
◼ Stratification
◼ Matching
◼ Regression (multivariable) models

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12
Q

What is restriction? what are the advantages and disadvantages

A

Eliminate variation in confounder (E.g., sex: recruit only male)

Advantages:
Effective, complete control of known confounder
Convenient, inexpensive, straightforward data analysis

Disadvantages:
Shrinks pool of available study subjects
Cannot evaluate primary relationship across confounder levels
May limit generalizability

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13
Q

What is randomization? Advantages and disadvantages?

A

Generate groups fairly comparable with respect to distribution of confounders in each exposure category

Advantages:
Control known/ unknown factors
Convenient, inexpensive, straightforward analysis

Disadvantages:
Usually applied to RCTs/ intervention studies
Works well only for large sample sizes

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14
Q

What is matching? Types? Advantages/Disadvantages?

A

Ensuring groups being compared are matches in terms of distribution of confounding variables. Type of partial restriction.

Pair matching: Each member of the control has to have the same value of confounding variable as the case group

Frequency matching: Frequency of cofounder is same in both groups

Advantages:
Easy, inexpensive, increase precision

Disadvantages:
Costly, time-consuming
Matching can no longer be evaluated as a risk factor

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15
Q

How is controlling confounding at analysis phase different

A

Must measure in study

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16
Q

Advantages of stratification and regression models

A
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17
Q

What is effect modification? How is it different from confounding?

A

Happens when an extraneous variable modifies the effect of the exposure of interest

Different because effect modification is not an artifact that can (or should) be adjusted away or controlled

It is a real aspect of the investigation

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18
Q

What is stratification and regression models?

A

Stratification: Divides samples into groups by levels of the confounding variable. Then adjusted for confoundings.

Regression: Produces adjusted estimates, can handle larger # of confounders, usually done with software

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19
Q

How do you know if uniform?

A

Visual inspection
Statistical test

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20
Q

What is primary prevention

A

Seeks to interrupt a destructive chain of causal events
For example: if people are becoming sick from drinking contaminated water, this is a modifiable link.

21
Q

What is secondary prevention

A

Identifying disease in its earliest stages (screening)

22
Q

What is tertiary prevention

A

Reducing negative impacts of established disease. Targets specific links in chains of causality that leads to better clinical outcomes

23
Q

What are the 4 frameworks which inform epidemiological judgements/assessments of causation

A

Web of causation
Causal pies
DAGS
Bradford-Hill’s Criteria

24
Q

What is web of causation

A

Population patterns of health and disease can be explained by a complex web of numerous interconnected risk and protective factors

25
Q

T/F it is possible to interrupt the disease by cutting one singular factors from a chain of various factors

A

True

26
Q

What is causal pie? Component/sufficient/necessary cause?

A

Proposes that sets of component causes combine to produce a causal mechanism.

Component: Single element of a constellation of components making up a sufficient cause

Sufficient: A cause that inevitably produces the effect; a minimum number of components causes which produces a disease (whole pie)

Necessary: A component cause which is a member of every sufficient cause for a disease

27
Q

What is DAGS? How to create DAGS)

A

Visual representations of qualitative causal assumptions
Diagrams follow strict rules

◼ To create a DAG one must specify:
 1) the causal question of interest, thus necessitating inclusion of exposure (E) and outcome of interest (D);
 2) variables that might influence both E and D;
 3) discrepancies between the ideal measures of the variables and measurements actually available to researchers;
 4) selection factors that influence which individuals are represented in the study population; and
 5) potential causal relationships among these variables (depicted as arrows connecting variables).

28
Q

What is consistency

A

The association is observed repeatedly in different persons, places, times and circumstances

28
Q

What’s temporality

A

Causal factor must precede the disease in time

The only one of Hill’s criteria everyone agrees with

Prospective studies do a better job establishing the correct temporal relationship between exposure and disease

28
Q

What are some of Hill’s criteria

A

◼ strength of association
◼ consistency
◼ specificity
◼ temporality
◼ biological gradient
◼ biological plausibility
◼ coherence
◼ experimental evidence
◼ analogy

29
Q

What is dose-response

A

A “dose-response” relationship between exposure and disease. Persons who have increasingly higher exposure levels have increasingly higher risks of disease.

30
Q

What is biological plausibility

A

Based on current biological social models, the association does not conflict current knowledge. The association is plausible

31
Q

What’s coherence

A

Similar to biological plausibility but engages a wider field beyond biology. Referring to the fit of an epidemiological estimate with results from any type of scientific research or theory

32
Q

What is experimental evidence

A

Used to be criteria for weighing causality. Current epidemiology uses experimental evidence to indicate that a study has employed randomizations. Provides strong evidence for causation, but many epidemiologic studies are observational.

33
Q

What is specificity

A

This criterion is rarely used. A given agent is always associated with only one disease and the agent can always be found with the disease.

34
Q

Critical appraisal steps

A

◼ Step 1: Identify the study’s research question or hypothesis.
◼ Step 2: Identify the exposure and disease variables.
◼ Step 3: Identify the study design.
◼ Step 4: Assess for selection bias.
◼ Step 5: Assess for misclassification bias.
◼ Step 6: Assess for confounding and effect measure modification.
◼ Step 7: Assess the role of chance.
◼ Step 8: Address causality.
◼ Step 9: Assess generalizability.
◼ Step 10: Report the critical appraisal.

35
Q

Importance of step 2: identifying the study design

A

Each design has strengths and weaknesses, identifying the design helps to organize critical thinking

36
Q

Red flags of ecological, Cross-sectional, case-control, prospective cohort

A
37
Q

What should a bias assessment specify beyond saying it has occurred?

A

Magnitude of bias, the direction of bias (over/underestimation)

38
Q

When will selection bias occur in a case-control vs a cohort

A

Will occur in a case control if the probability of selecting cases and controls depends on exposure in some way that differs between cases and controls.

Occurs in cohort if the probability of selecting exposed and non-exposed depends on disease in some way that differs between exposed and nonexposed

39
Q

two types of differential misclassification bias in case-control studies

A

Recall bias
Interviewer/observer bias

40
Q

How to minimize differential misclassification

A

◼ Exposure status should be assessed in the same manner for both cases and controls.
◼ Blinding interviewers and participants if possible
◼ Use of objective markers of exposure
◼ Verify exposure in other ways
◼ Use of diseased control group

41
Q

What is diagnostic suspicion bias

A

Type of differential misclassification bias.

Suspicion that the exposure is a risk factor could greater attention to detection of the disease in exposed subjects

Could increase sensitivity or decrease specificity for disease status is exposed

42
Q

What is Berkson’s bias

A

Synonym for selection bias in hospital-based studies

When the combination of the study exposure and outcome increase the chance that exposed cases are admitted to the hospital results in artificially elevated odds of exposure in cases

43
Q

What is selective survival bias

A

Occurs when prevalent disease cases are studied and if exposure is related to disease prognosis

44
Q

What is protopathic bias

A

Occurs when early manifestations of disease cause a change in the pattern of exposures in cases

45
Q

should confounding or effect modification be assessed first

A

effect modification

46
Q

How should a critical appraisal be reported

A

Written up in a few pages or verbally in 5 to 10 minutes

CHEP 350 (3 decks)

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