Bias,Confounding.

Question 1

What is loss to follow-up bias

Answer 1

• Individuals who are lost to follow-up may be different than those who remain under observation.
• Important consideration in prospective cohort studies and randomized trials.
• Even a small percentage of losses, if related to the exposure and outcome, can threaten validity of observed associations

Question 2

What is reporting bias?

Answer 2

Study participants may be reluctant to truthfully report an exposure that carries socio-cultural meaning. (Social desirability bias)

Question 3

T/F: Recall bias is the major bias in Case-Control study.

Answer 3

True

Question 4

What are the two major types of errors and their definitions?

Answer 4

Random Error: positive and negative fluctuations around the true value.

Systematic Error: a deviation from the true value (Bias)

Question 5

T/F: Identification and control of error is critical in epidemiologic studies

Answer 5

True

Question 6

Validity: Goal, Definition, Categories.

Answer 6

• *Goal:** to ascribe any observed association as truly the effect of exposure
• *Definition:** the degree to which an observation is free of error

Categories: Internal/External

Question 7

What is information bias

Answer 7

systematic differences in the accuracy of data on exposures and/or outcomes between study groups

Question 8

Potential for bias selecting into study groups

Answer 8

Question 9

T/F: Selection bias is one major source of bias for cohort studies.

Answer 9

False. It’s not because in cohort studies, exposure comes before the disease.

Question 10

Bias: two major types

Answer 10

selection bias

information bias

Question 11

What are the 3 types of information bias

Answer 11

1. Recall bias
2. Observer bias
3. Reporting bias

Question 12

What is the primary concern of information bias

Answer 12

misclassification on exposure or disease status

1. nondifferential
2. differential

Presence and direction of bias depends on the pattern of misclassification; requires exploratory data analyses

Question 13

Bias: definition, where it results from?

Answer 13

Def: systematic deviation of an observed association from truth

Bias results from systematically higher or lower counts of exposure (case-control) or incident disease (prospective study) in the numerator and/or denominator because of:

1. the process used to select study groups
2. differences in measurement accuracy between groups
3. confounding*

Question 14

What is recall bias?

Answer 14

It results from a difference in the ability to recall past exposure between cases (who are ill) and controls

Question 15

What is internal validity and what can influence it?

Answer 15

Accuracy of observations made within a study.
influenced by:

(1) selection of study groups
(2) measurement error

Question 16

What is observer bias?

Answer 16

When exposure or outcome status is known to the observer, assignment to outcome or exposure (yes/no) may be biased

Question 17

What is the response (participation) bias

Answer 17

If differences in characteristics between responders (participants) and nonresponders (nonparticipants) are correlated with exposure (or outcome), a biased measure of association could result

Question 18

What is Healthy Worker Effect and where does it apply

Answer 18

1. Def: Bias manifesting from selection of an external comparison (nonexposed) group that is less healthy than the exposed group
2. Traditionally seen as an issue in occupational cohort studies ( In general, people in the workforce tend to exhibit lower death rates than the general population)
3. Also applies to non-occupational cohort study designs that include an external comparison group

Question 19

What are the possible solutions to recall bias (2)

Answer 19

Validate case and control responses (sub-studies) 

Utilize cohort study or nested case-control study design

Question 20

T/F: Measurement error and misclassification are bias.

Answer 20

False. They are NOT bias, although they can contribute to association measures (OR or RR).

Question 21

Selection of controls may introduce bias

Answer 21

Question 22

What is external validity and what can influence it?

Answer 22

Accuracy of study observations in other groups. (generalizability)

influenced by:

(1) representativeness of study participants
(2) measurement error

Question 23

What’s the influence, source(s) of systematic error?

Answer 23

Threatens accuracy (validity)

Sources:

• Selection of study groups
• Measuring information
• Confounding* (Mike doesn’t agree)

Question 24

What are the possible solutions to interviewer bias (3)

Answer 24

1. Data gatherers blinded to group status 
2. Standardize case ascertainment & interview procedures
3. Monitor quality control during interviews (taping)

Question 25

T/F: For bias to be present, generally the error must be correlated with either the exposure or the outcome (need to look at the data)

Answer 25

True.

Question 26

Selection bias: Definiton, concerns in ca-co and cohort study

Answer 26

When the process of selecting cases or controls (case-control study) or, exposed or nonexposed (cohort study) results in an obscuring of the true association between the exposure and outcome.

Ca-Co: Is selection of cases and/or controls correlated with exposure status?

Cohort study: Is selection into exposed or nonexposed groups correlated with disease incidence?

Question 27

T/F: Bias threatens the external validity of study findings

Answer 27

False. It threatens the internal validity.

Question 28

What’s the influence, source(s) of random error?

Answer 28

Threatens precision (reliability) e.g. CI’s range

Source: Sampling error, measurement variability (inconsistency)

* Larger sample sizes reduce influence

Question 29

4 sources of selection bias

Answer 29

1. selecting study sample into study groups
2. selecting the controls
3. Cohort Study loss to follow-up
4. healthy worker effect