Bias and Confounding

Question 1

Validity

Answer 1

Relates to the absence of systematic error in a study

Question 2

a valid measure of association

Answer 2

a study will have the same value as the true measure in the source population, except for error due to random variation

Question 3

Bias

Answer 3

The extent to which a measure of association from a study differs from the true measure of association in the source population

Question 4

What causes bias?

Answer 4

Systematic error

Question 5

Internal Validity

Answer 5

the study result is valid with respect to the population under study

Question 6

External Validity

Answer 6

the study result is valid to a wider population beyond the study population and/or source population

Question 7

What is also called generalizability?

Answer 7

External Validity

Question 8

Study Population

Answer 8

the subjects in the study

Question 9

Source Population

Answer 9

Population from which the subjects were drawn

Question 10

target population

Answer 10

population to which we may want to generalize our results

Question 11

Non-differential bias

Answer 11

A bias that equally affects groups

Question 12

Differential bias

Answer 12

a bias that affects one group or more than another

Question 13

What are two general sources of bias?

Answer 13

Selection bias

Information bias

Question 14

Selection bias

Answer 14

error in selection of study subjects

Question 15

Information bias

Answer 15

error in measurement

Question 16

Misclassification bias

Answer 16

Misclassify animals

Animals with no disease are classified as diseased

Question 17

Confounding

Answer 17

an unknown factor distorts the relationship between the exposure and outcome

Question 18

Self Selection bias

Answer 18

studies based upon volunteers- may not be representative of the population as a whole

Question 19

Diagnostic bias

Answer 19

Diagnostic of disease may be influenced by the vet’s knowledge of the exposure and their expectation of disease

Question 20

Observer variation

Answer 20

Different observes interpret information differently

Question 21

What are some examples of Information Bias?

Answer 21

Observer variation
Deficiency of tools and technical errors
Recall bias
Reporting Bias

Question 22

Recall bias

Answer 22

Those affected by a disease have a greater sensitivity for recalling exposure

Question 23

Reporting Bias

Answer 23

Individuals with severe disease tend to have more complete medical records

Question 24

Selection Bias Examples

Answer 24

Diagnostic Bias

Self-selection bias

Question 25

Three condition a confounder must meet

Answer 25

Associated with exposure
Associated with the outcome
Not in the causal pathway between the exposure and the outcome

Question 26

How can you reduce confounding variables?

Answer 26

Match the study so the confounding factor is equally respresented
Restrict animals with the confounding factor
Randomize

Question 27

Stratify

Answer 27

Partition the results based on the confounding factor

Question 28

How do you reduce the confounding variable after the study has been completed?

Answer 28

Stratify