Class 13: Bias

Question 1

3 aspects to evaluate for internal validity?

Answer 1

Confounding or effect modification

Bias

Statistical significance

Question 2

Define bias

Answer 2

Systematic (non-random) error in study design or conduct that leads to erroneous results.

Question 3

Internal validity [based on deduction]

Answer 3

Valid relationship btw exposure and outcome

Question 4

How can you fix a bias once it has already occurred?

Answer 4

YOu CANT. Nothing can be done to fix a bias after the study end.

Question 5

3 elements of bias impact:

Answer 5

1-source/type
2-magnitude/strength
3-direction

2 and 3 are similar to confounding in the sense that it can skew magnitude and direction greatly

Question 6

2 main categories of bias

Answer 6

Measurement-related
And
Selection-related

Question 7

Measurement-related bias

Answer 7

Any aspect in the way the researcher collects info or measures/observes subjects which creates a systematic difference

Question 8

Selection-related bias

Answer 8

Any aspect in the way the researcher selects or acquires study subjects which creates a systematic difference between groups

Commonly seen: subjects not coming from same population OR not representative of entire population.

Question 9

What should you not do in a study

Answer 9

DONT DO ANYTHING THAT IS DIFFERENT OR CREATES A DIFFERENCE BETWEEN GROUPS

Question 10

Types of selection bias

Answer 10

Healthy worker bias: cohort studies

Self-selection/participant [responder] bias: differences in those volunteering and those not volunteering.

Control selection bias: case-control studies

Question 11

Bias in Cross-sectional studies

Answer 11

Newman bias: [selective survival]

More easily descriptive for longer lasting and more indolent diseases

Not effective for acute or rapidly fatal diseases.

Question 12

Measurement:

Subject-related bias

Answer 12

1-recall bias: differential level of accuracy/detail [hawthorne effect]

2-contamination bias: control grp subject accidentally gets treatment

3-compliance/adherence bias:different compliances
4-Lost to follow up bias: witthdrawl or lost to F/u rates…differences btw those in study and those withdrawling.

Question 13

Information/measurement:

Observer-related:

Answer 13

1-interviewer bias: interviewer influence on subject

2-diagnosis/surveillance (expectation) bias: different evaluation/diagnosis/observation btw groups.

Question 14

Misclassification bias

Answer 14

Error in classifying either disease or exposure status…or both.

source of measurement (info/obs) bias

2 types: differential or non-differential

Question 15

Non-differential Misclassification bias

Answer 15

Error in both groups equally…not as bad as differential-balanced error

Misclassification of exp. or disease is UNRELATED to the other

This moves the measure of asso. (RR/OR) Towards 1.0…reduces effect estimates of asso.

Moves closer to 1.0

Question 16

Differential Misclassification bias

Answer 16

Error in one group differently than the other.

Misclassification of exp. or disease is RELATED to the other

Bias moves measure of asso. (RR/OR) either direction from 1.0–can be either attenuating or inflation

Question 17

How to control for biases

Answer 17

Select the most precise,accurate and medically-appropriate measures of assessment and evaluation/obs

Question 18

2 main process interventions to control for bias

Answer 18

Blinding/masking:

Random allocation of observers/interviewers

Also: multiple sources to gather info, build in many methods to minimize loss to f/u